So I was considering the spell Sepia Snake Sigil, and a question occurred to me, one which also extends beyond just that spell into several related areas. (Areas which I'm not sure would all necessarily have the same answer.) Basically, if there is a task, spell or action that takes an extended period of time to complete, such that bonuses affecting the task can go up or down over the course of it, then how is the final DC roll at the end calculated?
For some examples, let's say we have Sammy the Sorcerer who likes to buff himself with Eagle's Splendor, giving him a +2 to his save DCs:
1) Sammy buffs himself in a quiet moment, and casts Sepia Snake Sigil on a letter he carries around in his pocket. Weeks later (when the buff isn't active) an enemy pickpockets the letter and tries to read it, triggering the spell. Is the save DC the value at the time of casting, or at the time of triggering?
2) In the middle of a pitched battle, while he's had his buff going for a while now, Sammy casts "Hold Person" on a foe and has it stick, locking the opponent in place. They keep failing the saves... but halfway through the spell's duration, his Eagle's Splendor runs out. Are the remaining saves in subsequent rounds done using the DC at the time the spell was cast, or his newly diminished DC?
3a) Later on, Sammy sees Billy the Bard start to cast Silence on an enemy spellcaster. Since it's a one round casting time, he gets a chance to take an action before the spell finishes completion, and casts his Eagle's Splendor on Billy. Assuming Billy does get the spell off, does the enemy caster save at the DC from the start of the casting, or the DC at completion?
3b) Either way, the Silence fails, so Billy tries to cast it again, this time with Eagle's Splendor from the beginning. This time it goes in the exact opposite way: he starts with the +2, but the enemy caster dispels his buff with Dispel Magic while he's casting. Does that make any difference if it's going down in mid-cast instead of up?
4) Sammy then decides he wants to get into crafting... but he hasn't been pumping Spellcraft nearly as much as he should have been. So he gets a Crafting Hat, a +2 INT headband set to give him max ranks in Spellcraft. He then puts it on, and immediate starts crafting something that takes him two weeks to complete. By the time he's done, 24 hours have long since past, and thanks to the headband he has max ranks in Spellcraft at the time he goes to make his check. Does he make the check with his current ranks at the time he makes the check, or is it affected by the fact that for one day out of the fourteen, he had a much lower skill level?
I don't know if there's a single, official method of resolving such situations listed anywhere, but if there is, I couldn't find it. Some of these I do have a gut feel about (the Sigil, at the very least, seems like it should use the higher DC given that it was completely cast) but I'm not entirely sure, and some of the others seem even less clear, so I figured I'd ask to see if there was some official RAW somewhere that I'd missed.
