If you have selected a repayment type with payment due while you are in school (Full Repayment, Interest-Only, $25 Partial Interest) then your first payment will be due 30-45 days after the loan is fully disbursed. If your loan will be paid in separate disbursements for each semester or quarter, the payment will be due when the loan is fully disbursed (after the last disbursement).
If you have selected Full Deferment, your first payment will be due after your grace period, which is 6 months after you graduate, drop below half-time, or leave school.