Help needed: Upgrade Tix to APs… theme park reservation?

Hi all,

The last time that I upgraded tickets to APs was before the park reservation system. When hubby and I are there in October, we plan to upgrade our tickets to APs, but my kids are not. All of us currently have 3 day PH tix for the weekend of Oct . 9-13, but our last park day will be Monday, Oct. 12. I know that weekend is busy and I am not sure whether it matters when I upgrade (other than I know it has to be before I use the last ticket on Oct. 12). Will I need a theme park reservation that weekend as soon as I upgrade? Example, if I upgrade on Oct. 11, do I then need a park reservation for Oct. 12? And will that be hard to get at the last minute with that weekend being busy?