Best thing to do is to thaw at room temp near the enclosure, not only does it ensure that the prey is thawed slow but it also help scenting which entice the snake too eat.

How long can it take, if it is a healthy (good body weight 2 years old) it can take a few weeks or a few months even a year because you have to practice tough love, if the f/t is not eaten do not offer anything else, of course you also need to use good judgment and know when to draw the line.