I tend to arrive early, since there used to be something several years ago at the time of ADR booking that said arrive 15 minutes before ADR time. But these days, email confirmations say that you should arrive at least 5 minutes ahead of time, and I can see this was the language used in both our 2016 and 2017 dining reservation confirms. I can also say that from our trip this past December, the staff checking us in felt we were on the early side for doing check in when we got there 15 min ahead ...and in only one case (out of 14 ADRs last trip) did it result in us being seated early. In past trips as well as the most recent, we found some spots wouldn't permit us to check in more than 15 min in advance and very few seated us early. We also had a few where we got there before the 15 min mark where they were either running on time or behind. While we made the choice to check in 20-30 min early, you waste a lot of time sitting there if they are running 20-30 min behind. So, whenever we return to WDW...IF we do any more TS meals, I'm just going to aim for that 5 min before window.