Both, from what I am getting out of it.
As for thawing: I leave mine out for 6-8 hours to thaw, then put them under a heat lamp with the heads facing the hottest part of where the lamp hits for about 15-30 minutes (depending on size).
A lot of people swear by water thawing, which can be done by putting the rodents in a bag then putting the bag in hot water. It's quick and effective, the temperature is often through the whole body instead of focused on the head, though.
As for switching: Give them 2 weeks, offer the rodents, 2 more weeks, offer again. And dont handle them in that time. Thats how I handled it.