Does anyone have any experience with going to Thyssen-Bornemisza Museum during the free entry times on Monday? Are the lines long? Is it worth going on another day and paying for entry? We would try this on Monday November 10th after visiting the Prado that morning. We plan to have reservations though for the Prado.
I went on a free day to the Thyssen and had no problems at all. It should take 1.5-2 hours to get through, so you'd be able to see it in the allotted time. It's a fantastic museum, preferred it to the Reina Sofia. It's much easier to make your way through than the Prado, and even getting tickets at the Prado is pretty quick, max wait time for me was 5-10 minutes.
The museum may be crowded, but I don't recall a line to get in. If I keep my own lunch quick, lunch time has often worked for me as a less-crowded time to visit anything.