What hours of the day are gyms the LEAST full/busy?

Best time would be early morning...most ppl are lazy and hate to come at that time. Besides its best for your body to workout at that time. cardio workouts and weight reducing workouts give max benefit at that time. Evening are the time when gyms are jam-packed.
And two free advice.
Good food, good rest and persistent exercise.
Don't over do and push yourself too hard. It will only damage your body.
Schedule your workout so that you exercise a muscle only twice a week. For example, if you are adopting a 6 day workout one day rest routine, exercise your biceps only on day 1 and day 4. Rest of the days the muscle is given time to recover and rebuild.