Lesser Vigor lasts for 10 rounds + 1 round/level, up to 15 rounds. If I use Extend Spell on it, is the limit still 15 rounds?
I found the following Sage Advice/FAQ quotes on the playground.
The main quote:
Main 3.5 FAQ, Revision 06/30/2008, p. 40
Q: The Vigor series of spells (CD) raise an interesting question. Does the built-in maximum duration of each spell limitation override the effect of the Extend Spell feat?
A: Yes. Extend Spell still increases the spell’s duration, but only up to the spell’s listed maximum duration. Use either the normal maximum duration or the doubled duration, whichever is less. If a 7th-level druid used Extend Spell on her Vigor spell, the duration could not increase beyond 25 rounds.
Which is corroborated by a second quote:
Main 3.5 FAQ, Revision 06/30/2008, p. 92
Q: The Mass Lesser Vigor spell has a fixed range (of 20 feet), which makes it eligible for the revised Persistent Spell feat in P.G.. Does that mean a 17th-level druid could use a 9th-level spell slot to give nine creatures fast healing 1 for 24 hours, or does the built-in limit of 25 rounds make that pointless?
A: Unlike Extend Spell, Persistent Spell replaces a spell’s normal duration with a new duration of 24 hours. In this case, the effect overrides the normal maximum duration of the spell, so it would indeed grant nine creatures fast healing 1 for 24 hours (a pretty reasonable effect for a 9th-level spell).
The FAQ itself can be downloaded here; I have amended the quotes with the latest revision.
The FAQ is not necessarily authoritative, and sometimes of dubious quality; it is up to you whether you choose to follow its ruling or not.
If you do choose to follow them, then the rulings are clear:
- Extend Spell doubles the normal spell duration of a spell, up to the specified maximum duration if any.
- Persist Spell simply overrides any duration to 24 hours.