Adding two rounds to the casting time is acceptable, I guess, but frankly I'd rather keep it as a spell (to force Wizards to have to take the option ). You could make it something Sorcerers just do, though.
To answer your question from before about spells with a 24h casting duration: It will be done on a case-by-case basis, but it's worth noting that there are some spells that get a little stupid when Permanency is applied to them, all of which have 24h durations and no expensive material components (all from the Spell Compendium):
Anticipate Teleportation (technically this doesn't matter to anyone but the stingier optimizers, but the last thing I want to do is make Rocket Tag even stupider)
Delay Disease (indefinitely)
Energy Immunity (permanency all energy types for total immunity)
General of Undeath (permanently increasing the HD cap of undead you can control by an amount equal to caster level... Innocuous in most circumstances, but cheesed out when combined with everything else, utterly deserving of the 8th-level slot)
Incorporeal Enhancement (see General of Undeath, but I'm on the fence about this one)
Resistance, Superior (+6 permanent bonus to all saves)
Undead Lieutenant (OK, I take it back. General of Undeath is piddling compared to this. Create multiple Permanent Undead Lieutenants for a NI control undead cap)
However, I have decided to allow the following spells as a consequence of this review (all, also, from the Spell Compendium):
Force Chest (technically 24h/level, but still)
OK. On to PHB!