Twice is enuf
Some people brush 5 or more times a day.
Some brush once or not at all :( i recommend twice a day. Once in the morning after breakfast, so as not to offend your coworkers or fellow students. Also..Brush at night before you go to bed. This will get out all debris tha could lead to decay. This is the more important of the two. In the middle of the day...You can swish with water.