Hello,
Usually it is best to switch to rats as quickly as possible. However, that said, I have never had much trouble getting my hog islands to eat rats. I kept both my hog islands on mice until they were eating large sized mice then I switched them to appropriate sized rats (just bigger than weanling rats). So I think you would be fine keeping your hog island on mice for awhile. However, I have only raised two hog islands so my experience with them is limited. I also have dumerils and jungle carpet pythons that I switched ASAP or began feeding them rat pups because some of mine have shown preferences for mice. Anyway, just my two cents, if you have any questions let me know.
Erin