It really varies from one person to another, I have 4 that are still on mice and I started feeding 2 adults at around 500 grams.

BP can do just fine on mice there is not obligation to feed rat, you need to feed what work and is convenient for you.

As for adult they either get a small rat 45/65 grams or 2 to 3 mice (which is the equivalent to a small rat depending on the mice size).