Cleon
Legend
I'm not that bothered about the balance issues. It's intended as a "plot device" more than anything else.
The original adventure features a small group of four priests chanting to perform a ritual to break their boss Ythog-Nthlei out of a magical imprisonment. I was interpreting this as being equivalent to a dispel seed so needed the ability to allow a group of four priests to case that epic spell.
Requiring Epic Spellcasting as a prerequisite would prevent any number of basic priests casting the dispel seed, since only epic level characters can acquire that feat.
I think making it take hours/days would make the chant take way too long. I would considered minutes instead of rounds though.
If I wanted to add additional time constrictions to it I'd be more likely to have something like "Finishing the spell exhausts the ability to use chant magic of all the priests involved. Recovering their ability to use chant magic takes X days it the chant magic was a regular spell or Y weeks if it was an epic spell."
Oh, and as for the example bear in mind that it would require 30 basic priests to produce a Caster Level of 50 needed for a DC 100 epic spell.
If we cut out the CL bonus it'd be practically impossible for a non-epic priest to create an epic effect which rather defeats the point of why I wanted to give them the ability.
Actually, that reminds me of something. I was going to add "The Aid Another action cannot be used to assist this Spellcraft check" but forgot to do so, otherwise all the priests in the group except the caster could stack Aid Another bonuses on the 'caster'. For example, in the aforementioned 30-priest group you'd have 29 priests Aiding for a +58 bonus, which would make the DC too trivial.
Although in any case I'd have no objection to adding a note that epic usage is at the DM's option and they should be careful about what epic spells they can produce or require additional conditions (special items, "cosmic alignments" or the like).
But how about greater command, flame strike, slay living?
