We’re in the same boat with our dependent care FSA

What I do is consider the expense as a monthly bill (since our daycare costs are more than we allowed by law to put into an FSA anyway), then I have the reimbursement as a line of income. My husband gets paid biweekly, so we have to budget based on when checks come in anyway (rather than just monthly), so that’s just considered another line that we have to budget based on timing. I’ll often try to have the daycare check writing co-incide with that reimbursement, but it doesn’t always happen that way. We usually get our “invoice” from the previous month the first week of the following month (but must be paid current at all times, so it’s not just like a bill to pay) and I receive my FSA reimbursement pretty quickly, so it’s put into the spreadsheet to be anticipated around mid-month. I know many people that don’t request reimbursement monthly, but we don’t really have room in our budget to upfront the money for months (or a year) at a time.
It’s a pain because it’s a reimbursement, so you basically always have to budget it a month ahead — but it works for us!