On the Dash 8 it is MEL Cat. D, i.e. 120 days (or hot all of summer, cold all of winter...)
I didn't want to imply that dispatch without APU is impossible on the CRJ/Fokker, it's just more of a nuisance because you need a jet starter for every turnaround. I'd imagine you'd have some restrictions on minimum thrust if you fly the CRJ in icing conditions without APU. (Fokker doesn't use APU bleed while airborne.)