It is usually easier to get your snake to eat one larger meal than multiple small meals.
Guessing without weight, should be a pup to small weaned rat, or two to three mice.
I have a couple +1000g snakes that are mousers and have been their whole life, I just keep offering till they refuse.
Agreed. It's easier to switch earlier than later, too. The longer they eat mice, the tougher the switch is. You, then, risk having to feed a large adult female 6-8 mice every week.