Please help with the itinerary for Barcelona in May 2020

Are you arriving in Barcelona after an overnight flight? I would be in no condition to visit $25 tourist sights on my arrival day. I would instead try to do some outdoor sightseeing that afternoon.

About 90 minutes inside Casa Batllo and Casa Mila was right for me, except that at the time of my visit (2016) Casa Mila had a special exhibition upstairs on Gaudi's other buildings outside Barcelona. There were video clips, etc. I spent a lot of time there. Note that both of the houses will be utterly packed; you could spend all day in one of them, trying to make pictures that don't have other people in them. Don't even try.

The Sant Pau site is the one where I needed over 2 hours. It has multiple buildings and nice grounds. A couple of especially pretty rooms are upstairs in the main building, which falls at the end of the self-guided tour. You don't want to have to skip those.

I would definitely not skip the Palau de la Musica Catalana to walk around Barceloneta. I didn't find the latter all that interesting.

You have very little time in Barcelona. Do not waste any of it on the Ramblas. You'll probably end up on it at some point; there's no need to go looking for an overcrowded, pickpocket-infested commercial street.

Thank you very much acraven!

I will have 18 hours flight including transit time and yes, I see your point. I'll try my best to rearrange my itinerary.

I'm thinking about walking around Barri Gotic, the Cathedral and El Born on the first day as you suggest and visit Casa Batllo, Casa Mila and Palau de la Música Catalan on the second day instead. Can you please recommend time slots for all these three places?

For May 3, I'll get to Park Guell early so I'll have more times at Hospital Sant Pau.

Thank you again.

You should also know that May 1st is Labour Day in Europe. In Barcelona, and the rest of Spain, it is a public holiday for us. A number of shops and restaurants will be closed, but it should not be a problem in the main touristy centre. Most major tourist attractions will be open, but smaller museums and attractions may close early. You may encounter a delay in public transport, albeit slight, you may also encounter some manifestation/blockade actions by labour and/or separatist groups.

As acraven mentions, May 1st is a good day to just walk around and explore, especially since it is a public holiday.

In my experience, Casa Batllo and Casa Mila are more crowded than the Palau de la Musica Catalana (tour capacity is limited; book in advance to be sure you're on an English tour). Casa Batllo was a bit worse than Casa Mila for me. I'd buy a first-time-slot ticket for one of the two houses, then hit the second house, then find food (lunch is late in Barcelona), then take the tour at the Palau de la Musica Catalana. I wish I knew whether the Gaudi exhibition at Casa Mila is a permanent thing. Without it, you'd probably be fine booking the second house 2 or 2-1/4 hours after the first. It will take longer to get down to the Palau de la Musica Catalana, and you'll need to get food before taking the tour there, so I'd try for a longer gap after the second stop. Length of the gap needs to take your eating preferences into account. Will you grab a pre-made sandwich or sland somewhere, or will you take advantage of an interesting-looking Menu del Dia you see advertised along the way?

Since Casa Batllo is closer to the Palau de la Musica Catalana than Casa Mila, there's something to be said for starting at Casa Mila. However, the first thing to do is check the hours of the English tours at the PdlMC. I don't think the tour takes more than an hour; it might be less than that.

Thank you so much Carlos.
I'm aware of Labour day so at first I chose to go to some Casa because it's open on that day. However, as you and acraven suggested that I should do outdoor sightseeing. After consideration, I agree to wander around Barri Gotic and El Born.

Also, Thank you once again to acraven.
I think I have to start with Casa Batllo and then Casa Mila, since I got an open-time ticket at this casa. For Palau de la Música Catalana, the English tours continue until 15.00. I can have lunch before I get there.

Thanks to both of you, my solid plan is coming!