Reservations are not needed. The code “GR” only means that groups (10 people or more) need a reservation. Individual travellers do not need that. Look at the code legend below the train details.
If you buy a normal ticket it is a good on any train on the route for a whole day. So you can leave earlier or later, and stop over at your own discreton. A Chur - Tirano ticket is also valid via st. Moritz, so you could even have a quick look there.
Some windows do open. The IR trains on Chur - st. Moritz have a nice photographers lounge at the locomotive end, with large windows that open.
Are you starting your day in Chur? If you are starting somewhere als you do not need a separate ticket to get to Chur. Just buy a normal ticket from wherever you are starting out to Tirano via Chur.
