At least twice a day if you have a fenced in yard for him/her to run in if no fence then I would say 4 to 6 times a day. Because they are small they need to go to the bathroom more often. It may...
If this is a dog then i suggest once or twice a month, mainly after long walks because they can get very muddy. also keep a towel handy so you can wipe its paws of all the mud.