With online banking the first time you pay a bill, the process starts slower the first time you pay a certain payee, while your bank and the payee's electronic system establish an electronic relationship. The second month, a payment to that payee should have (about) a 2-day window. Your online account will say how much time to allow. Some payees don't have electronic connections, and your online bank will send them a manual check each time. In my case, I'm told to allow 5 days for manual payments. (Funny, one of my manual payments is to another bank, for my car payment!)
If you can't pay a certain online bill earlier than 3 days before due date, arrange to pay that bill directly with the payee. That's the only way to prevent the situation of a late fee or ding on your credit record, if you're recorded as paying late. Sometimes a payee's posted payment receipt date will differ from your idea of what that date is. The payee may only post payments during certain hours, and after that time, payments received will be credited next day. So don't try to cut it too close, unless paying by phone directly, or at a payee's place of business.