If you have the auxiliary cooler as well, it would likely take even longer than without..... it's after the radiator cooler.... which serves to warm the fluid when its really cold out.

According to what I have read, trans fluid temp needs to be 108 or better, to engage overdrive..... There is no way on gods little green acre my trans got that warm in one mile of driving, when it was sub-zero temps out..... and I have the aux cooler as well. (on both trucks.)