I concur with JimmyBean42. We have had some meals where it's in and out. No problem (Even a Character meal) As an example we had an early ADR for Akershus Breakfast. It almost seemed like we were rushed out. From the time we checked in until we left (including the "Picture Taking" with Belle before we sat down) was probably about an hour.
Conversely we had an ADR at Crystal Palace one day and had to wait almost 30 minutes past our ADR time to get in. Then it was probably almost 90 minutes (or longer) before all the characters finally made it around to our table.
Lastly we had ADRs at Mama Melrose's. While we waited about 15 minutes past our ADR to get into the place, once in, we were done and out (leisurely) in about an hour.
I guess it really depends upon the location, your expectation (are there characters and do you want to see them all?), time of year, time of day, weather (believe it or not), and probably a whole lot of other factors.
My suggestion is to plan for upwards of 90 minutes but make sure your plans after your TS are flexible enough. So don't plan a 12:30 Lunch at the Crystal Palace with a 1:30 FP+ at the 7DMT because you might miss it (even if the window is an hour long on the FP+)