My daughter and I will be in Barcelona for a week in January. Sans car, of course, so we'll take the train one day to see the Dali Museum in Figueres. It's too early now to buy the train tickets, but I think I've figured out the Renfe website well enough to get what I want: two return tickets. It appears that I'll have to buy the tickets there and back for certain times. If we have to stick to that, so be it. We'd prefer, however, to have a bit of flexibility for our return trip. Will our return tickets be valid on that same day at any time?
Comprehensive advice, there. Only one addition: I'm guessing one draw is the Theatre Museu Gala Salvador Dalí.
You might consider buying your ticket to the Dali museum in advance, to avoid standing in line.
https://www.salvador-dali.org/en/museums/dali-theatre-museum-in-figueres/