If you are only interested in pursuing it as a hobby, then enough is enough when you decide to move onto other interests. Nothing wrong with that, and if you are able to get some pleasure out of it by going back and playing later on, even better!
That said, many people I have come across say that they wish they had continued working on the piano - so even if you find a few pieces you enjoy and spend a little bit of time on them, it will help keep those skills at a level you are happy with down the road. It doesn't need to be a certain amount of time every day, but just when you want something to do, sit down and make some music!