when do you submit for reimbursement?

My dependent care account that we'll use for DS1's preschool this year is a funded-per-paycheck account so they don't provide a spending card up front, but I'll have to submit paperwork online/fax/email for reimbursement.

If any of you use the same, do you do it as you go? Or do you just wait until your max point of contribution and get one lump reimbursement? And in what form do they send your reimbursement payment?

Thanks in advance!