Listen To Your Dr. You need to follow the instruction of your orthodontist. Elastics (rubber bands) are prescribed to make specific tooth movements. Your orthodontist gave you the elastics and told you how long (number of hours per day) you should wear them. If you forgot, call your orthodontist.
24/7. Unless instructed otherwise, wear them all the time. If they are not in your mouth they are not moving teeth. And when not worn it takes extra time to restart movement. So try to wear elastics 24/7, even during meals. Ask your orthodontist for instructions unique to your course of treatment.