Neil B.
Google
An excellent visit, advance purchase ticket worked out perfectly.
I can share my experience here as the other reviews were very helpful to me. Note I visited in November.
I checked the weather, cloud cover and visibility on windy.com and then booked a ticket for the next day for a 10:00 am timeslot. The confirmation email suggested arriving at 09:30 am.
I arrived around 09:15 am and there was a queue of around 200-300 people queueing to purchase tickets. The staff directed people who already had tickets to the left hand side windows (don't join the big queue by mistake, go to the main entrance and say you have a ticket), where you collect your actual ticket, by showing your confirmation email. This is your ticket up and down the train so don't lose it.
I then queued for maybe 10-15 minutes to get on the train. The train departed around 09:50 am so you didn't appear to be restricted to a specific booked train. As others have said sit on the right hand side of the train, in the direction of travel, for the best views of Rio during the ascent.
Everything else is straightforward, no other ticket required, spend as much time as you like and then queue up and get any train back down.