May 24, 2016 - 2:19 PM
It's not an ideal day trip as it takes 4.5 to 5 hours one way (to St. Moritz). But it can be done. You'll find schedules in the timetable. There's actually a direct train from Andermatt to St. Moritz via the Landwasser viaduct (the Glacier Express), but it only departs later in the morning.
If you can make this a two day trip it would be more enjoyable I think. The ride across the viaduct only takes 20 seconds or so. So it's quite a long day for only 2 x 20 seconds of viaduct. Although the rest of the trip is very nice as well. Still, with an extra day you could walk from Filisur to the viaduct to take pictures, for example.
Another option is to go as far as Bergün or Preda only, and perhaps visit the Albula railway museum in Bergün: www.bahnmuseum-albula.ch.