I have long known that Trenitalia will let you book 120 days out for the Freccia trains. So I usually set a calendar reminder in advance of our trips and log on early in the AM to get a good price 120 days out. I buy outgoing and return tickets separately as the purchase windows open. This is an essential strategy to getting the best fares. BUT I discovered today that the trains are opened for ticketing on an hour-by-hour basis. I wanted a return from Venezia on Dec. 10 about 09:30. At 07:45 there was one train available at 07:25. Hmmm, I thought, I wonder.... I checked at 10:00, and the 09:30 train had opened up. It has proceeded so throughout the day. As I write this at 14:30, trains up through 14:25 are now available, with later trains shown as outside the 120 days.
This knowledge may help you as you try to get the best fare.