I plan on visiting El Escorial on a Friday afternoon May 1st. Do i need to buy tickets ahead of time because of long lines or can I buy them upon arrival?
I visited on a Thursday in July, we just showed up and had no problems. A small (less than 5 minutes) line at the entrance was all, and once inside, not at all crowded. In May I would expect even less. I did have to check a small back pack, but they have an attended, secure locker room for that.
May 1st is a holiday in Spain, but you should still be okay. Trains and buses might be more full than usual. Check government websites to see which places are open.
We just walked up and bought them at the time. No delay at all. And it's such a huge place, it would take a mighty big crowd to feel any impact from it.