You can pour additional arcane energy into your conjuration spells in order to vastly improve the duration.

Prerequisites: Extend Spell, Spell Focus (conjuration), Novice Conjurer, 5th level

Benefit: Whenever you cast a conjuration spell that has been affected by the Extend Spell feat, you may choose to spend twice as long casting the spell in order to extend the spell's duration to 5 times the normal duration, rather than twice the normal duration.