Thank you very much Krist. I cannot tell you how much I appreciate this! People where we are staying just suggesting something similar. We’re staying about 15 minutes from the Filisur station. They recommend that I book a round trip ticket from Filisur to Tirano. When we get to St Moritz, get off of the train we are on and get on the BE, using our purchase the seat reservations.
The train from Filisur leaves at 8:01 and arrives in St Moritz at 9:01. My BE train leaves at 9:17. Does that sound about right?