UT tix latest time to order?

I plan to order our tickets from UT but I am waiting for my sis to give me her share of the money. DH said this trip had to be paid upfront if she and I were to take it. Our FPP date is 9/1. Since I have never ordered tix from UT I am wondering how long I can hold off and still be sure I will get them by then. I am hoping to hold off until 8/15 for ordering them if I can.

UT says 10 days to ship, you can pay more for faster shipping. So go from there. This is my first time ordering myself, but I am confident, I ordered Wednesday and they were shipped out for Friday, now I am just waiting.

Thanks @Jedilogray. It sounds like I should be safe ordering at 15 days out. Hopefully I can order a few days earlier.