ritual:when is the vis spent, what if you stop, when to roll

Related to the topic of casting a ritual, I'm in need of clarifications and do not find anything in the core rulebook, nor by a quick research on this forum. Apparently, "ritual casting" brings too much results and because of the slow forum these days, it's a pain in the ass to read all those 126 pages of results.

  1. Can someone remind me if there is something in the RAW about the moment the vis is spent when you cast a ritual spell?

More precisely: you start casting the ritual; do to the vis immediatly disappear, or only at the end of the 15' per magnitude of the spell casts only?

  1. and related to the same topic, if you decide to stop casting the ritual, is there any sort of circumstance, like let's say, failing a concentration check while casting a circle/ring spell?

  2. do you roll at the start or at the end of the casting time (example: you have special circumstance "day" (which may also be a "cyclic magic positive"). You start an aegis level 40 (2h casting) 1h before dusk, and it finishes 1h after dusk. Special circumstances do apply or not? [noble's parma on the special circumstances/cyclic magic positive applying on ritual spells.]

For question 1 I have no clue; intuitively, i'd say end; for 2 I would have said no. 3 I'd say at the end since I seem to recall that when you have slow caster, your roll at the end of the 2d round.

But my haste to answer in that way is what drove me here to ask fellow players. I may miss something, somewhere and I think there is much more in a lot of players' head than in just my own.

Context of the question : imagine there is an aegis spell on your covenant. Your enemy plan to replace this aegis by his own; in our saga IRL another SG said (and that's what I'm evaluating now) that at the moment he starts casting his own aegis, our own aegis is dispelled (with maybe no malus for casting his own, if the roll is made at the end since the other aegis is gone at the start).
My point would be that if the vis is spent at the end, and if there is no consequence for stopping casting a ritual, that rule is gamebreaking.
It remains dangerous/tedious at least if the vis is spent at start (because we also house rouled that to dispell a Ritual, you need a ritual and so, using vis for a PeVi or vis for a ReVi is not much changing... except that the ReVi is more useful to you than the PeVi) and there is no consequence.

If there are consequences, it would depend of those. If this is a botch roll with as many dice as vis involved, it may be okay because no magus would risk 1+4 or more botch dice in an unamical environment, I think per principle (exceptions may occur).

But if you are able to start an aegis, thus cancelling another aegis, then stop and not spend the vis... aegis are as good as useless in serious situations. (Especially if you are a "normal" magus confronted with a Marched one.)

I'm assessing that house rule checking these questions, because discussing that first house rule would require me to have evidences of gamebreaking situations it creates. And before bringing the topic, I like to know more than just my own impressions or feelings.

  1. The rules on Ritual Magic on p81 of the core rules do not say when the vis is spent. In my face-to-face games, we always house ruled it is spend at the start of the ritual, in order to encourage magi taking precautions before casting rituals, and to emphasise the riskiness of casting a ritual in the middle of an adventure. I suppose you could house rule that vis is used “as you go” – ie one pawn every 15 minutes.
  2. This is a hard one as normally you don’t cast rituals you don’t plan to complete. I would count stopping a ritual the same as if you were disturbed and failed a concentration roll – roll to see if you generated a botch, otherwise ignore the results. Then again, if you visualise how magi gain practice experience in spell mastery for Ritual spells is that you can practice parts of the ritual over and over, maybe you can stop rituals without penalty.
  3. I would roll at the end, but “cyclic magic” explicitly states the bonus has to apply for the whole period to gain it, but the flaw applies if any part of the activity falls during the penalised time (pages 41 and 52 of the core rules). (The examples given are for lab bonuses over a season, but the same applies to day/night). I would say the same should apply to special circumstances.
    The example you give has one obvious flaw: While you can override someone else’s magical effect with your own magical effect, your magical effect does not exist until you’ve finished casting the ritual. If you cast a level 20 aegis, and then someone wants to cast a level 25 over it, they have to complete the level 25 ritual in full before their effect comes into force.

I agree with Darkwing in preferring the vis is spent to begin with. Once you start to cast the ritual it commits the vis.
For one thing this is for balance, so casting rituals is not trivial, where you can just change your mind before being done.

As for when to roll, I’d say at the end. You. Don’t know if it works until you’re done. If you know too early, you can stop, and that ruins the feeling of rituals for me.
A bonus needs to last for the entire casting time to take effect. Same goes for penalties.

If interrupted I assume that counts as a Botch. Again, rituals must be a big thing.

But why would an enemy magus casting a new Aegis end the new one? IMHO both would be there, but only the highest magnitude having an effect.