The frequency of changing your hamster’s sand bath depends on how often he uses it and this may differ depending on his breed.
In general, this is the frequency of changing sand baths according to your hamster’s breed:
Dwarf hamsters: Every 1 - 2 weeks
Syrian hamsters: Every 3 weeks or when cleaning the cage
Other breeds: Every week
Additionally, if you see wet clumps in the sand, you should also remove them.