Dali Theatre Museum tickets in advance- question

I was on time for my museum visit so cannot say with certainty what happens if you are late. However, the usual deal is that the ticket is worthless if you miss the entry time. That's sort of the point of selling tickets for specific times rather than just for a specific date.

My visit was on a Friday in mid-May this year, definitely not yet peak season. I bought my ticket online a few days in advance and had no problem getting my preferred time slot (the first one, giving me a few minutes in the museum before it got really crowded with one or more French tour groups). I haven't read here that the museum sells out far in advance, but I wouldn't be surprised if early time slots sell out, and there's a substantial risk that if you show up in the morning without a ticket you'll be sold a ticket for 3 or 5 hour later, which would rather mess up ones day in a place like Figueres with limited local attractions. If you show up ticketless in the afternoon, you may find there are no tickets left for the day.

For what it's worth, I found hotel rooms comparatively cheap in Figueres.

If you need to eat at an odd time, you may have luck at Cafeteria Astoria, which is visible from the bus stop used by the bus from Figueres Vilafant station. It's at the corner of La Rambla and Pujada del Castell. It is not a cafeteria in the US sense, just an informal restaurant that remains open through the afternoon. Not special, but OK for what it is. I do not recommend the restaurant in the Duran Hotel. It considers itself a sort of gourmet spot, but my meal was disappointing in several ways--and I rarely complain about restaurants.

Plan to get there early. It's worth walking around the building to see it all from the outside. If you get there very early, you'll be able to visit the Clock/Jewel Collections first. (separate building, included in your ticket)

Fwiw, I went with my family of 5 from Girona, took the train to the farther station (fast train - I think its ~ 1 mile from the museum), we tried to get there before opening (so timed our walk to train station + train ride + walk from train station), and this was in July. We arrived ~10 minutes before the ticket booth opened. There was a minimal line. All told, the whole thing was really easy and crowd-minimal. I dont see the need to plan as much as you are but maybe thats because my 'plan' for doing it first thing was in the mark. The museum never seemed to get crowded though. Then we ate lunch in the plaza nearby (not the one directly adjacent) and then walked back to the train station.

The web site for Dali Theatre Museum provides information regarding the number of tickets available on a day and the time slot. In mid May 2019 I checked site 1-2 days ahead. We walked from the train station, arriving 10-1100 to purchase onsite tickets. On the day of the visit I had a general idea what time I would arrive using public transportation. We trained from Girona using the Roadalie. We purchased round trip in Girona. The gentleman in Girona told us we may need to pay an upcharge on the return due to the label on the return train. We asked at the return desk and paid the uncharge for the return. I prefer to be spontaneous unless the site is a must see site.

Sitting in a train station while waiting is a human museum. There were young people hanging out for no real reason. A cyclist changing clothes and eating while his support had a huge suitcase for him. The cleaning staff were mopping and well cleaning! I wonder what they thought of 2 americans hanging out? The train arrives and everyone disperses.