Eh, 10min is fine to me. I see this like COR's merit JA Fold, which has a 15min recast without additional Fold merits - and Bust lasts longer and is more harmful to a COR's essential purpose.

Use Cool Down if you screw up trying to go overboard nuking, or if it's really important not to overload and you've just activated a fresh puppet. Otherwise, ignore it. It's really a minor addition. I doubt most decent PUPs are going to be doing a lot of riding the Cool Down timer in any case...