Most snakes will eat within a day or two of owning them. Just most of us advise people to wait so they don't think something is wrong with their snake because it's not eating. I also wouldn't deal with mice, my baby 53 gram BP can eat a rat fuzzy no problem. I fed him a rat pinky just because it's a bit smaller and with him being small. Your BP being 4 months old and eating hopper mice is really distrubing to me TBH. A lot of factors come into play with this but did you ever ask the local breeder why mice instead of rats? I would personally try a f/t rat pink, fuzzy or pup if you're BP is big enough. That way you don't waste money on mice when you can be feeding him rats. Who did you purchase your snake from?
Regarding f/t, where are you from? I'll give you more information with everything once I know the rest.