A tidbit of interest from Lands of the Nile. I'll try to avoid spoilers.
I'm working from Serf's Parma, so I may get some détails wrong, but here's the geist of it.
There's an insert describing a situation in which magi can be subjected to multiple sunrises/sunsets, which should cancel their parma magica.
Now, what's interesting is that it says that the parma gets dropped, unless the magi concentrate on it one round to maintain it.
As far as I remember, there was nothing suggesting that this was limited to that situation. I may be wrong, but I remember getting the distinct feeling that this could be done at any sunrise/Sunset.
Do anyone agree/disagree? Maybe this is a recent breakthrough from our bonisagus sodales?
=> It looks like the Parma Ritual takes about 2 minutes to complete, but that, once up, you just have to concentrate briefly at Sunrise and Sunset to avoid that 2-minutes time window of vulnerability, thus closing a big hole in Ars Magica, possibly changing how we think wizard's war are fought. Coincidentally (or not), it would also align parma with what happens when you pick up concentration from an item subject to the "flicker" effect at sunrise/Sunset.
I've never previously heard anything about being able to maintain parma by concentration alone rather than reperforming the ritual. I think I would have seen something else written on the subject (but you never know I can miss stuff too).
Now the ritual is about 2 minutes as are sunrise and sunset. I've had my ears up since the 1990's to see an official judgement regarding whether or not one could, with paranoia and crackerjack timing, keep your parma up without a flicker. I've not seen anything. Personally I allow it but I try and make it challenging for my players to pull it off.
A similar question arises about Sun-duration spells in general - if you have a ward against demons cast, and a horde of demons surrounds you - as the sun rises up, and you cast the next instance of the ward, can you establish the new ward before the old one fades, or will your ward flicker, letting the horde in?
My instinct is to say that you can establish the new spell in the "twilight" of the old, so that there is no flicker. There is some period in between, when the old spell still works, but a new one can be cast and last a full duration. This corresponds well with the rules for constant effects (quoted above), and feels less cheesy. BUT - I don't know of any rules to that effect, either for Parma or for regular spells.
Does the sun rising or setting take about duration diameter from the time that the orb first touches the horizon until it is completely beneath it, or is an instantaneous change say when the sun disappears completely?
The first interpretation allows for a magus to cast a spell during "this" sunset the will last until the next sunrise, the second doesn't.
Having a sunrise and sunset with duration makes it more similar to duration moon (until both the old and new moon have crossed the sky) and duration year (both the summer and winter solstices have passed). in that you can cast a spell during the night of the full moon or during the winter solstice and get no "flicker".
The real question to ask is what makes for more fun around the table? Is having this weakness going to lead to interesting stories about showdowns at sunset or is it going to lead to bitchy annoying stories as the PC's get screwed over at sunrise repeatedly?
Is it more fun to tell stories about the PC's working to get their timing right or PC's working to deal with the inevitable gap in their magic?
My gut tells me that it's typically more fun to give more power to the PC's, but i don't like making decisions with my gut.
Serf's Parma on this one (and when did it become Noble's Parma? Aren't serfs good enough for us anymore?), but wasn't the Curse of Thoth cast during the Schism War just after sunrise to catch the Diedne without their Parma? If it's easy enough to keep your Parma up without a flicker, don't you think that most of the Diedne would have done that (especially during a war)?
Ah. Noble's Parma is not the same as the Serf's Parma.
serf's parma - I may be wrong, because I am at work and my books are not
monk's parma - I may be wrong, because my books are at work and I am not
noble's parma - I may be wrong, because my books are in the next room and I am not (implicit: and I'm too lazy to go into the next room)
As an argument against a moment of concentration being all that is necessary I believe that it is very strong.
As an argument against the possibility that someone who is prepared and waiting for for sunrise to begin so that they can perform their parma in synchronicity with the rising sun will, if they do it right, be able to keep their parma up with no flicker it is a bit less strong. Depends on how easy it is to pull it off.
While it's never been made explicit in 5th edition, this was exactly how it was in 4th (explicitly by some book I can't remember, possibly WGRE). Define sunrise/sunset as the time intervals (each lasting D:Diam) when the sun is only partially above the horizon. Then a D:Sun spell or a parma ritual completed at some time during sunrise would last until the end of the following sunset. Similarly, a D:Sun spell or a parma ritual completed at some time during sunset would last until the end of the following sunrise. This gave every magus some slack (about two minutes) during which to renew his magical defenses.
In a similar fashion, we always assumed that D:Year spells cast on a solstice or equinox, and D:Moon spells cast on a new or full moon would have about a day of "overlap", though I can't recall if it was ever made explicit (I believe it wasn't).
Would you mind giving the reference now? ArM5 p.85 Parma Magica is unequivocal about two minutes needed to cast the ritual. Sourcebooks should not interfer with that general rule, unless they cover very specific situations or introduce Virtues.
This is - by ArM5 p.99 Effect ModificationsConcentration - an item maintaining concentration on a D: Concentration effect. The wielder needs not to trigger a recast then, but "must concentrate on the effect a few moments to perpetuate it until the next sunrise or sunset". See ArM5 p.105 Sample PowersSpeech for a nifty example.
People often sleep through sunrise, and magi often have Aegis of the Hearth running as well. Parma MR is often higher than the Aegis, though, because Parma and Form Score adds together while Aegis and Form score do not add together. Curse of Thoth with +41 Penetration probably got through most Aegis protection, while an awake magi with Parma up probably has a (Parma x5) + Vim + Magic Aura greater than 41, unless they are young (for magi).
A magi during a Wizards March should be paranoid enough to time his Parma, but people are people, and Curse of Thoth was something nobody expected could be done (non-Hermetic magic that targeted a group of magi without an Arcane Connection to each member). And sunrise would have been different at each covenant location, so it's debatable how many Diedne they actually managed to catch at all.
or it could be an enhancement to the PM discovered after the wizards war...
or (not having the book in question I would not know...) it may only apply to certain situations where you apparently have multiple sunrises and sunsets in a day...
This discussion inspires the idea of a minor breakthrough to unleash in a game. Not as a carrot, but as a new development that starts to circulate in the mid 13th.
A new seperate Arcane Ability. It adds to resistance, stacking like a Form. It also grants one special trick per point. Such as...
Concentraition Maintenance (as discussed above)
Share Parma with a token (so they can leave your sight)
Parma Fold (one of the varients from True lineages)
Fast Parma (takes a single round instead of 2 minutes)
Midnight Parma (like the Nyktowhatevers from the Tremere)
FWIW, the Curse of Thoth ignores the idea that the sunset doesn't happen the same time everywhere. Not saying you have a point, but saying that Curse of Thoth, as used against the Diedne has some additional problems...
If you read the RAW, yeah, Form scores and Aegis do not stack, nor does Parma+Form+Aegis. Except if the spell is cast within the Aegis. It doesn't make a lot of sense to give someone an advantage for casting within the Aegis, while giving the defender a significant advantage in defense at the same time. IMO, the rules suggest that the Aegis attempts to resist the spell cast from outside, if it doesn't resist the spell, then it goes against the Parma+Form, having much of the power stripped from spell and tested against MR at the new, reduced level of the spell. The example provided, also doesn't consider an MR of a target with an Aegis, The Seven League Stride could be an AC (or sight) to a specific place, and not a magus or other individual with MR. I know stripping penetration from a spell cast outside of the Aegis isn't RAW, if you read the Aegis description literally, in the single instance of spells cast from outside of the Aegis, but it is more consistent with the behavior of stripping half the level of the Aegis when within the Aegis. It doesn't make sense that an Aegis is less effective against spells cast outside of the Aegis.
With regards to the penetration example of the Curse of Thoth, it's important to note that the Diedne were winning against the rest of the Order. One doesn't win wars safely ensconced behind defensive fortifications. IMO, the penetration total affecting many Diedne doesn't speak to the issue of the Aegis combining with a magus's personal MR. Also, it's written that the remaining Diedne retreated, out of reach, and it doesn't say how many were involved. Removing a sizable percentage of a fighting force in a surprise maneuver, which you know nothing about the specifics and how easily it can be repeated makes sense to retreat to defenses, and come up with a different plan...