Email their help email address to ask - they get back to you fairly quickly! I *think* they have to have all the LOR's. I know mine lagged a bit in getting in, even though I submitted my application already and my app didn't get mailed until later. Although they are working on calculating your GPA (took them about a week or week and a half for mine) and it definitely doesn't get sent out until that is finished. After that finished, it was maybe a day or two later when it was mailed out, but all my LOR's were also in by then.
I had to really pester my letter writers toward the end. Some of them had had the info for a couple months and still not written it. As soon as I started dropping by their office just to check nicely or emailing them to make sure they had the appropriate links, the letters got written 🙂