Some people know a few restaurants they want to try, either by learning about them, friends' recommendations, pics on the internet. I think most would prefer evening TS vs lunch TS because of the Florida heat diminishing your appetite in mid-day. Choosing a TS restaurant at the theme park also implies you'll be at a certain park that day, if you don't have park hoppers. So now your overall Disney schedule is involved in meal planning. You might want to break it into components: If I'm at MK, I want to try for X, Y or Z. Same for DHS, AK, EP. Some new places don't take reservations: Hollywood Brown Derby Lounge at DHS, Tutto Gusto and Spice Road Table at EP. Resort restaurants can be good for last-minute reservations, like Grand Floridian Cafe (GF), The Wave (CR), Whispering Canyon Cafe (WL), Captain's Grille (YC), Sanaa (AKL) for late lunch/early dinner, etc.
There's a lot of time between 180 days out and your check-in. As you hone your plans, the various pieces will begin to fall in place. And you can always keep trying to get the restaurant you wanted which had no availability at 180 days. 45 days before check-in there are many who cancel their Disney trip, bc that's the cut-off for full package payment. That means more openings for you.
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