You can take as much you want becouse is no side effect or over doze, however by taking 900mg per day will cost you to much.
For general health 200mg per day, for athlets (tim sports and drug and stimulants free 300mg) per day. 100mg first in the morning, 100mg after training and 100mg before bedtime, if the tim travels and have to play the game in a diferent time zone it be good idea to take one right before the game. Weght lifters 400 to 600mg per day.