I take 1000mg Vitamin C tab in the morning with my first meal, 1 before working out, 1 after working out, and 1 before going to bed. That's more than enough and covers all your basis during times when your body needs the extra Vitamin C the most.
When you awake, the hours right after training and before going to bed, are the most critical.
The hours after training is critical because your body has been heavily stressed through
intense exercise, and your body's immune system is the weakest during the hours post workout. So vitamin C supplementation is important at this time.
When you awake from a night's sleep, your body is in a
catabolic state, where you have not eaten anything for several hours, and at this time, your body's immunity is low.
Taking vitamin C (along with a multi-vitamin) is good insurance for recuperation and growth while you sleep.