I don't know what's best but we do all at one time, but we take away some time after a short nap. I know that it can take a few days for them to get used to the new atime so if you want to try, hold for 3 days before changing, that's the advice we got and it always worked for us! They can get some ot naps at first but you should be able to see results in three days if short atime is the problem.