Is there any reason this wouldn't work?

[Yogibear41]

Say I have a high level Planar Shepherd (high enough to transform into outsiders from his chosen plane) Working with another character capable of casting Summon Monster II.

The Planar Shepherd wildshapes into the Kocrachon Devil from BOVD, which among its many SLAs has Liquid Pain at will.

The other character casts summon monster II to summon a lemure, which according to Fiendish Codex 2 page 9 are "in constant physical agony"

Said Planar Shepherd then uses Liquid Pain as a standard action on said Lemure to produce as many doses of liquid pain as it can before the summoning ends(with a max of 10 does due to the Lemure having a Con of 10)

Is there any reason I couldn't use this strategy to produce a decent amount of Liquid Pain in down time?

[Kelb_Panthera]

Unfortunately, SLAs take the same casting time as the spell they mimic unless otherwise noted. Liquid pain's casting time is 1 day.

[Yogibear41]

"Using a spell-like ability usually takes 1 standard action
and provokes attacks of opportunity unless otherwise noted.
If the spell-like ability duplicates a spell that has a casting
time of less than 1 standard action, the spell-like ability has
that casting time"

From the rules compendium, if the SLA takes a day to cast, what is the point in having it as an at will ability?

http://archive.wizards.com/default.asp?x=dnd/rg/20040413a

also has SLAs as specifically being a Standard Action unless the ability specifically says otherwise.

[Kelb_Panthera]

"Using a spell-like ability usually takes 1 standard action
and provokes attacks of opportunity unless otherwise noted.
If the spell-like ability duplicates a spell that has a casting
time of less than 1 standard action, the spell-like ability has
that casting time"

From the rules compendium, if the SLA takes a day to cast, what is the point in having it as an at will ability?

http://archive.wizards.com/default.asp?x=dnd/rg/20040413a

also has SLAs as specifically being a Standard Action unless the ability specifically says otherwise.

Those citations don't actually contradict this one; http://www.d20srd.org/srd/specialAbilities.htm#spellLikeAbilities

It explicitly says "A spell-like ability takes the same amount of time to complete as the spell that it mimics (usually 1 standard action)."

The casting time is usually one standard action because the overwhelming majority of spells have a casting time of one standard action.

The at-will designation matters because, if the spell is disrupted, the creature can begin again immediately instead of having to wait until the next day.

[Endarire]

This also wouldn't work due to GM Fiat if that happens.

[daremetoidareyo]

Couldn't you just be a caster and use attune gem, create infusion, or craft rune?

[Deophaun]

Under the general spellcasting rules the target isn't determined until the spell takes effect at the end of casting. You could start casting the spell 23 hours, 59 minutes, and 42 seconds before your buddy cast SMII, provided you can stay wild shaped that long. The question is does the "Over the course of a day" sentence require the target to be there. It doesn't make it explicit, so...