residency requirement for US citizenship

My 5 year permenant residency requirement for applying US citizenship will be in August. Since I can file form N-400 90 days before I reach the 5 year requirement, I am thinking of filing in May. Does anyone know whether there\'s disadvantage of applying 90 days earlier? I heard stories of people filing 90 days earlier wait a lot longer than those who apply after actual 5-year requirement is met.
Any info will be appreciated. Thank you very much.