Your can select the targets of your spell long after you have cast the spell.
Benefit: When casting a spell that has one or more targets, you need not select all targets as you finish casting. Instead, you may select the targets up to 1 round/caster level after the spell has actually been cast. The spell is still limited by its normal number of targets and the spell's duration is still measured from the time of casting. A postponed spell uses up a spell slot one level higher than the spell's actual level.
Normal: You must select all targets of a spell the moment you finish casting.
Does the above feat have the potential to be broken?
An example of intent: I cast postponed haste (CL 7th) on the party. I select the 4 party members and we all benefit from the effects of haste immediately (and for the following 7 rounds). Two rounds later I summon 3 monsters who are all also targeted by my postponed haste spell (the monsters and the party members benefit from the spell's effects for another 4 rounds).
If I were to summon monsters on round 9, I could not haste them without casting haste again (even if I had additional targets to spare).
What do you think? Is it balanced or did I overlook something critical?