I tend to decide on that depending upon the weather......if it's a bit warm, I'll put it in the 'fridge but if it's cooler I leave it on the side to defrost.
I have always (for about 30 years) cooked ALL my meat in the slow cooker, it is not necessary to defrost any of it at all just take it straight from freezer and chuck it in.
I just put it on before i got out to work and its well cooked when i get home (as with everything else i cook in slow cooker!) - not sure how much less than a whole day it would take?