The Magician's Tower

Is Heart of Vapor/Flames/Ice/Stone on the same timer? Ie. can I use them exclusively or will they all red-out and be unusable at the same time?

I'm thinking Flames and Vapor are most useable for their + up to 50%dd, reduce hate up to 50%. But before I spend the 22aa on them both I'd like to be sure I can use 2 of them within the 22 min timer.

I'm sure they don't stack, but if I can at least get some use out of them both it'd be worth the AAs. Otherwise I know I'll only use one, which would be flames.

And I assume it's the same for Core of xxx later on?

Fire Core and Vapor Core share a timer. Ice Core and Stone Core share a timer as well. It should be the same for the Heart of series.

so i guess most mages have fire for offense and earth for defense, available exclusively.

For the most part. I find myself using Ice more than Stone. The VoA ranks of Vapor Core has increased crit damage.