Well he was about 700 grams or a little less when I started the conversion. It took about a month and a half. I hear they can go a few months without food but im sure that after a month or 2 your boy will be hungry enough to take the rat. I cant give a definite answer on my methods because I went from live mice straight to f/t rats so I had him in a scented enclosure for the first 3 feedings. Although, I have a feeling that if I didnt use the scenting enclosure he would have taken the rats either way.