Bernina Express

The Swiss change their timetables once a year, on the second Sunday in December.
The new timetables are normally issued late October / early November, showing the times up to December the following year.

The Italians change their timetables twice, in December and June. In each case the times for the next 6-months are published ~1 month before changeover (not as early as the Swiss).

In both cases, for planning purposes just assume next year's times will be similar to this year's

I assume you mean "Milan to Tirano". Tirano is the southern end of The Bernina route. Turino is somewhere else.

Italian train schedules update in early December and early June, but the schedules seldom change very much. You can buy discounted tickets 120 days in advance although that varies as the schedule updates approach.

Ditto Swiss trains in terms of schedule changes (don’t change much year-to-year) but I do not know when they post.

Are you looking to plan your itinerary or wanting to know when you can buy tickets?

Tirano - oops!!