Something you might want to keep in mind is that sometimes party activities start before the party. The last party we went to was in 2019, so take that for what it is worth, but party activities started around 5:30 or so. We got a picture with Moana, shopped for party merch, took a Magic Shot, did the walk behind MSUSA and got on line for Lotso all before the party officially started at 7.
Another thing you might want to also consider is that if your party priority is something that tends to be very popular (like photos with Jack and Sally or the 7 Dwarves, etc.) those lines start long before the party does. Getting out of dinner at 6:00 could leave you with a bit of a wait at the start of the party.
Since there will be quite a few parties before yours, I would make your ADR, but pay attention to the reports and reviews of the parties as they come out. If things seem to be trending where you might benefit from not having the TS, just cancel, and change your plans around. A lot of it will depend on your personal preference and what you plan to get out of the party.