I've recently read an article about time management for microstock photographers, i have confronted it with a real situation and discovered these rules work fine (from the experience of other photographers):
60% of your microstock work time should be dedicated to making photos.
15% will be used to edit your photos.
20% for adding relevant keywords and descriptions.
5% use it to choose categories.
This formula works even if you dedicate 10 hours per day for microstock work or 2 hours per month. And don't forget : Time is money