7-10 days. I start off with 1/8 cup fo the new for 24-48 hours, if he does okay with that then I doublt to 1/4 for 24-48 hours, if he does okay with that then I double to 1/2 for 24-48 hours, then 1 cup so on and so forth. He does the best on the Pacific Stream version of TOTW or the Bison and sweet potato formula of NB. CA Natural gave him the worst reaction of any of the foods I've ever tried so personally I stay far far away from that one. For us I've stuck with NB LID or TOTW Pacific Stream (he's allergic to the proteins in the other versions), but now I'm trying Earthborn's Primitive to see how that's going to work. It's been not quite 24 hours, so far so good hoping it keeps up.