Belt of Temporal Summoning (3.5e Equipment)

Belt of Temporal Summoning
You must wear this belt for 24 hours before it takes effect. Whenever you cast a spell that summons a creature, its duration increases as if you were of a higher level (+1 level for minor, +2 for greater, +3 for major).

Prerequisites: Craft Wondrous Item, Able to cast a spell that summons a creature.

Cost to Create: 500 gp, 12exp, 2 days (+1), 4,500 gp, 112exp, 18 days (+2), 13,500 gp (+3) 337exp, 54 days.