Jun 15, 2017 - 1:25 PM
in reply to tierneyjohn
Hi John, and welcome to MySwissAlps!
The main reason for doing this trip would be to take the Bernina Express scenic route: Milano-Lugano-Tirano-St Moritz (8 hours one way, partly by bus). There is really only one departure daily that would work: Depart Milano 08:10, arrive St Moritz 16:11.
Another scenic route, mainly by bus, is the Palm Express route (Milano-Lugano-Chiavenna-St Moritz). There is only one departure daily. You would need to depart Milano at 10:15 and would arrive in St Moritz at 15:45.
To get back to Milano the same day, you would need to leave St Moritz by around 17:00 and travel (partly by bus) St Moritz-Thusis-Bellinzona-Milano.
If you want to explore the possibilities further, you can do so by using the Swiss Timetable: