When you want to see. Using glasses more will not hurt the function or anatomy of the eye. You should wear the glasses whenever you wish to see better. This could be full time.
When they help. With the exception of very few instances, glasses are not mandatory. They will help you see at certain distances and if feel improved vision is important full-time wear is recommended. The only exception would be for amblyopia (lazy eye) therapy for small children - they should always wear their glasses as prescribed.