If you are asking this question, as little as possible. Beginner beekeepers cause a hive more damage than good every time they open the hive. So in this case the Spring, early summer and fall inspections are probably the best! If you have gained some experience, you can eventually get to the point where you can open hives weekly and manage them intensively without causing them harm. Often you find beginner beekeepers open the hive every three days and stare optimistically into the hive hoping that something has happened. This causes the bees more stress than is neccessary.