YES, time mages are an excellent addition to any party. Their skillset is, at least. As far as time mages themselves go, I think they have a bit less MA than a Wizard, but a bit more HP. Even if Haste was the only spell they ever knew, I'd still love them for that. That's not even counting Short Charge and Teleport.

Short Charge would (should, anyway; I've never tried) cut Cloud's Limit charge times in half, and Haste would let him get more AT's to start charging his Limits in the first place. Haste doesn't affect charge times, though, just how often your AT comes up.