Train tickets can now be booked much further out (for some routes). Since the Tren Maya first started running we've been limited to buying tickets just 1 week into the future which has been the source of a great deal of confusion in this group.
For the Cancun - Palenque routing it seems I can now book tickets months into the future (but not for all tickets). On other systems such as in the UK or Spain it's common to be able to buy tickets for popular scheduled runs sooner and then as the travel date approaches they'll open up more tickets on in-between runs. It seems from my very rudimentary research that they're going to follow this formula for the Tren Maya.
I can currently book tickets on all trains between Merida and Cancun for the next month, but if I go out 4 months I can see 3 of the 5 trainsets. This could mean:
1) The current schedules will not change in the near future
2) Major changes aren't happening soon
These might sound similar but let me explain the nuance.
For #1 it means that the Tren Maya folks are happy with these scheduled runs so these scheduled runs will probably exist far into the future no matter what happens.
For #2. In the future we expect there to be major schedule changes once the ERTMS signalling gets done which will allow more trains running closer together. A LOT of things are waiting on this to happen. Allowing the purchasing of tickets months in advance may mean that they don't expect ERTMS to be done any time soon (or it's not high priority).
This is a good move no matter what the motivation may be. I think it's fairly safe to say that if the train schedule that you want is available next week it will also be available in 2 months but you may have to wait to buy the tickets. I set notifications on Google Calendar to remind me later to buy the tickets for train systems in Europe. This way I get the tickets as soon as they're available. Using a similar system for the Tren Maya may make sense as well.
When I checked the Cancun to Chetumal trains and the Chetumal to Escarcega train I was not able to purchase a ticket more than a week into the future so there may be schedule changes coming still. We'll see
.
Updated info on Tren Maya isn't easy to come by. ¡Gracias!