Greater Time's Arrow

Transmutation
Level: Occ 4, Sor/Wiz 4
Components: V,S,F,M
Casting Time: 1 standard action
Range: Touch
Target: The arrow or bolt touched
Duration: Permanent (D) (see below)
Saving Throw: Will negates (harmless, object)
Spell Resistance: Yes (harmless, object)

As Time's Arrow, but the spell is nearly permanent, lasting until it is triggered. The missile attacks with your base attack bonus + 4.