Wishbound Arcana says:
At 1st level, the wishcrafter can use the wishes of non-genie creatures other than herself in place of the normal verbal components of her spells... A wishcrafter gains a +1 bonus to her caster level when using a creature's wish as a verbal component in this manner, but cannot include herself as a target of such spells.
Strictly by RAW, the time limit is "the same turn" (less even than "the same round"). The wishcrafter is using the wish as a verbal component of the spell, and verbal components have to be provided as the spell is cast; you can't speak a spell's verbal components in the morning and cast the spell silently later that day. Some spells that could be used to "grant" V's wish in the same turn would be:
silent image or a similar illusion spell (producing paperwork showing B's out-of-the-way-ness);
teleport or greater teleport (to take the party to B);
modify memory (to make V think B is out of the way [normally only usable by bards and a few clerics]);
However, it certainly seems like a thematic and fun house rule to make the time limit be "until the wishcrafter has an opportunity to grant the creature's wish."