Same action as it takes to disbelieve an illusion, presumably, whatever that is.
To disbelieve an illusion a creature must "study it carefully or interact with it in some fashion", so I'd use that wording.
My best guess is this is a Move Action, since the
Spot skill says "Trying to spot something you failed to see previously is a move action", which sounds similar to studying something closely, and interacting with an item is a reasonable match to the "In most cases, moving or manipulating an item is a move action" in the SRD's
Actions in Combat.
No objection to making it a cleric spell if it's OK with Shade. Maybe even a bard spell, too.
Fine by me.
Assuming the spell's the same level for all three classes, that revises
solipsism to:
Solipsism
Illusion (Shadow)
Level: Brd 6, Clr 6, Sor/Wiz 6
Components: V, S
Casting Time: 1 standard action
Range: See text
Effect: See text
Duration: Concentration
Saving Throw: Will disbelief (Special, see text)
Spell Resistance: Yes; see text
You use material from the Plane of Shadow to shape quasi-real illusions of one or more creatures, objects, or forces. Solipsism can mimic any sorcerer or wizard conjuration (summoning) or conjuration (creation) spell of 6th level or lower, except its duration is as long as the caster concentrates. The illusory objects, forces, or creatures created by
solipsism appear to be transparent images superimposed on vague, shadowy forms.
Solipsism is the opposite of normal illusions in that creatures must make an active effort to believe (rather than disbelieve) in the illusion to be affected by it. The spell has no effect on those who do not believe. The objects and creatures "conjured" by solipsism become real to those who believe in them, with all the normal properties their form and function allow. Thus, a solipsistic
wall of stone bridging a chasm could be crossed by the caster and those who believed. All others would see the caster apparently walking out onto nothingness. Likewise, a solipsistic
summon monster spell can create a creature that can carry believers on its back, or attack believers to cause real damage.
The caster of
solipsism automatically believes in the reality of their solipsistic illusions. Other characters must deliberately try to believe in the illusion and succeed at a DC
19 Will save to be affected by this spell. A failed save means the character cannot convince themselves of the illusion's reality and the
solipsism has no effect on them. To believe in the illusion, a character must study it closely or interact with it in some fashion (this usually requires a move action). A character can make a single attempt to believe each round.
Once they successfully believe in the
solipsism, believers will continue to be affected by its "conjurations" for the duration of the spell. Believers can automatically stop believing in the
solipsism as a free action, but if they do so and decide to "re-believe" they need to succeed at the Will save again. The effects of solipsism continue for as long as the spell's caster maintains concentration. The caster can dissolve discrete elements of the illusion (e.g. a single creature out of a group, or one arrow in a quiver, but not part of a single object or creature) while continuing to concentrate on the rest of the solipsism, but such dissolved elements can not be re-believed into pseudo-existence except by casting the spell again.
Objects automatically fail their Will saves against this spell.
