I'll tell you what I do. I know a lot of people do it the same way I do, but there are varying methods of thawing out f/t mice.
First of all, I will turn on the tap water while i'm preparing my mice. I turn the hot on and let it run for a while. I'll grab a mouse out of the freezer, and i'll either put it in a zip-loc bag, or i'll just let it thaw in hot water by itself. I get my thawing container (I use a deli cup - it's your preference what you use.) and make sure the water is really hot. I fill up the container, and put the mouse in. I usually leave the mouse in there for around 10 minutes give or take a few minutes. (The larger the mouse, the longer it takes. 10-15 minutes is average for me, though.)
After the 10-15 minutes is up, I will dump out the water and feel the mouse with my bare hand. (I know some people think that's gross, but you can wash your hands - it really doesn't hurt anything.) I gently squeeze the belly and make sure that it's warm, and that it isn't hard. Then I feel the head. If the head of the mouse is hot, then it's ready to go. If it feels luke-warm, it goes back into the water for a few more minutes.
After that, I feed my snakes. Voila!