We are visiting Tivoli on Sept 13th. I bought tickets to Villa d'Este for the evening when it is lit up. However, we probably want to go there during the day as well. Do we have to buy tickets ahead of time which forces us to select a time. We don't want to be boxed in. That is why we didn't take a tour.
When we were there in May you just walked up to the window and purchased the tickets. The line was only about 10 people long.
When we were there a couple of years there was no time restrictions on the tickets. Bought at the window and walked in.
When we go there - good choice, it is wonderful! - we just turn up and go in. It is very easy to get tickets at the gate.