...Idk you guys might be over exaggerating. I think the reason SE made it a 10 minute timer was because you can give it to other people in your party... and it would kindof chipin your 2hr if you had instant cast every 3 minutes. I don't think SE wants you guys to be able to cast instantly very often (they think that's what fast cast is for).

The way I see it it's just a skill to help you on long recast spells like raise or help other mages cast instantly... then again I don't play rdm so take my opinion with a grain of salt.