Yes, you can bentonite the secondary. However, it's always best for the wine to be warmer to do this and is why you always see the advice to do this in the summertime.
Your best bet is to do it in the primary. It's a lot less hassle than in the secondary and you'll see the wine beginning to clear in the secondary even after a couple days! We use alot of bentonite because we make many fruit wines with no water addition so our musts are always very dense. It clears wines beautifully, and you also get the additional effect of heat stabilizing the wine so that you have no or less precipitates in the bottles when they're chilled. Be aware that when you go to transfer to the secondary, your wine will be very milky--just ignore it--this is how it's supposed to look after bentonite dosing.
Before we used bentonite in the primary, our chief hobby was trying to clear wines in the secondary. I hate fooling around with stubborn wines in the secondary.
I would let the must come to temp on its own. Stir it around every day to help it thaw. And when you're ready to start the ferment, be sure there are no fruit pieces with mold on them because sometimes this will happen. Just disgard them.