From late April to early August a colony must be inspected at least once a week and an inspection will take 30mins per hive plus 30mins preparation time. During May/June when you are undertaking swarm prevention measures it may take longer. Everytime you go to your hive you will have pre-planned the activity and you will take the right equipment.
During the winter you should check every so often that the bees have sufficient food and the hives are intact. This will only take a few minutes because it is essential that the heat is not allowed to escape from the hive.