If it's totally frozen, I would give it at least thirty minutes in hot water. The F/T I feed Dixie (med to large rats) thaw like that for at least an hour to an hour and a half.

I highly recommend a UTH or flex watt for belly heat. It will help improve your humidity. Before I became a multiple bp owner... I used infrared heat and lights (years ago)... had all kinds of humidity issues. Switched Dixie to a UTH, removed the lights and the humidity stays perfect with only a weekly misting.