I run my tap really warm, then fill a glass with it, then pop the mouse in. I leave it for about 10mins, then empty the water, refill it, and give it another 5 mins to warm through before feeding it. Iv so far only had to feed pinkies and fuzzies, and this has worked fine. Maybe when I increase the size of mouse I may have to leave it in the warm water a little longer. To check its defrosted properly, if you gently squeeze its head or belly, you will be able to feel its temperature throughout, ifs its even slightly cold, I heat it up more! Good luck though, you'll soon find your own way that suits you best.