Needs review
Source: Pathfinder: Advanced Class Guide

Description: You have learned a trick that makes your spellcasting more flexible.

Prerequisites: Spell Mastery, Prepared Arcane Spellcaster

Required for: Improved Flexible Wizardry

When you prepare your spells each day, you can choose to keep a number of spell slots equal to your Intelligence modifier (minimum 1) flexibly prepared. Instead of preparing a single spell within each of these slots, you can partially prepare two spells. Anytime after you prepare these flexible slots, you can spend a full-round action to finalize one slot, choosing one of the two spells to be finished and fully prepared in that slot.