I think the longest a Moon duration spell can last is one month, if it is cast right after a new moon or right after a full moon. If it's cast right before a new moon, for example, then it only lasts the two weeks or so until the next full moon.
In the case of a casting on June 21, 1227, the next full moon is about June 29 and the next new moon about July 14, so it would last a bit over three weeks.
Indeed, and with about 2 weeks between a new moon and a full moon, and 2 weeks between a full moon and a new moon, there isn't any way to add up to 2 months.
Brain fart, never mind, carry on. I'm not even tipsy tonight.
Personality : Chaotic, same as the flaw. Not suite what the other question is asking. Lab came this way.
First go at trying to create Theraphosa's baby spider chilluns. Complicated by the fact that between designing Theraphosa and now, I picked up Hermetic Projects, which includes rules for insects. (Which, tangentially, is weird, because spiders show up in a lot of other places -- Lion and Lily, Magi of Hermes...)
Further complicated by the fact that I see no way to increase an animal's size except through Magical Qualities. As Theraphosa is Might 15, Size -2, with three (3x) Major Magical Quality:Gigantic, I needed the kids to be at least Might 5. I take small solace in the fact that they live in a magic regio and don't have any actual powers (beyond Enchanting Music), so they're not that much harder to kill.
I'm of two minds about them as Might critters. I don't like the idea that they'd contain vis, have magic resistance etc. On the other hand, they're a horde of giant gorram spider/sirens. So maybe they need to be at least a little magical.
Spider Sirens (Aggressive Crawler) Might: 5
Virtues
Magic Animal
Essential: Perfect Balance
1 Enchanting Music
1 Free Expression
1 Supernatural Lore (as Arcane Lore)
FLAWS
Essential: Compulsion: Cannibalize Our Wounded
Inherited: Anchored to the Mountains
-3 Bound to Magic
Magical Qualities/Inferiorities 5
3x2=6 Gigantic x 2
1 Virtue: Unaffected by the Gift
-1 Limited Gestures
-1 Susceptible to Deprivation
Characteristics: Spider +3, Brave +1
Cun 0
Per -1 Age: ??
Pre -6 (+3)
Com -4 Size: -6 (base -15)
Str -12
Sta +1 Confidence:
Dex +3
Qik +12 Afflictions:
Combat Init Qik 12, (Damage: 1,2,3,4,Dead 5+)
Attk: Dex 3 + Brawl 3 = 6(grapple),
Def: Qik 12 + Brawl 3 = 15(grapple)
Soak: Sta 1 + Exoskeleton 3 = 4
3 Athletics (climbing) (+3 climb) (+6 to avoid falling or tripping)
3 Awareness (food),
3 Brawl (grapple),
4 Craft: Spidersilk (webs) +3art
4 Enchanting Music (curiosity)
4 Hunt (ambush)
3 Music (singing) +3art
4 Stealth (hide) +3 to hide
3 Survival (home terrain),
Qualities
Ambush Predator: If it has successfully crept up on its prey, it automatically wins Initiative in the first round of combat and gains a +3 to its Attack Total for the first round only.
Camouflage: Add +3 to all rolls to hide, whenever the creature is not moving.
Crafty: Increase Cun to +0
Grapple: The creature may make a grapple attack instead of a normal attack. This attack may only be employed against an opponent that is less than or equal to the creature’s (Size + 1). See Non-Lethal Combat (ArM5, page 174) for rules ongrappling. If the creature has another natural weapon (such as a bite), it may add its current Grapple Strength to its Attack Total in subsequent rounds, until the opponent breaks free. The creature must defend against any opponent outside the grapple with its Grapple Defense (see Natural Weapons Table, below).
Loathsome Appearance: Presence drops to –6 or +3 when attempting to scare or intimidate an opponent.
Skilled Climber: Add +3 to all rolls involving climbing.
Thick Fur/Thick Scales: Add 1 to Protection; this Quality stacks with the Tough Virtue and the Tough Hide Quality.
Tough Hide: Add 2 to Protection; this Quality stacks with the Tough Virtue and the Thick Fur Quality.
Venomous: Compare the creature bite’s Attack Advantage to the victim’s Protection (not Soak). If the creature’s Advantage is higher, then the victim suffers the effect of the venom, regardless of whether the bite inflicts an actual wound. The Ease Factor is 9, Incap (see ArM5, page 180) (compared to Theraphosa's 15, Incap)
Web-Weaver: Not listed in book.
While I was rambling about various future plans for deviousness with my mirror, Kid Gloves came up with a brilliant solution to the Eternal Repetition Warping problem.
This is especially appealing to me as I plan to spend a lot of time exploring Intangible Tunnel's value in the Canaries game.
That is an absolutely wicked idea! Genius in its simplicity (after a fashion).
Tweaked the Spider Siren brood some more.
I decided to give them the classic "Eat our Wounded" flaw, in case some desperate Odysseus needs to get away from them. I also weeded out their skill section and filled out their combat stats.
Just in case, you know, anyone wanted to tame piles of them at a time and give them to our grogs as WatchSpiders.
They may be a little too big and strong. I'd give them Might 3, a grog-level character.
But I think the best way to handle them might be as a swarm 
You think we're in a Medium Powered campaign? Grogs for High Power are suggested Might 5, which is why I figured it would be okay.
Technically, Grogs can't take major Qualities like Gigantic.
Where are the swarm rules?
Legends of Hermes, IIRC. You'll love them. The chapter about the maga who researched the 4 realms.
And yes, IMO, given both their description and their abondance, they should be low in power (especially as we based our familiar's might on a medium powered campain). Might 5 would be fine for a few children, but is, IMO, too high for a such a horde.