Venice to Compatsch

Ok, I calculate you must leave Verona Porta Nova at 3:02 pm, gets you to Seis at 5:21 pm in time before the list closes at 6 PM. Earlier departure is at 1:50 pm at arrives at 4:21 pm.
Better check yourself.
https://www.sii.bz.it/en/siitimetablesquery
http://www.valgardena.it/en/hiking-biking/walking-trekking/lifts/

It is the 170 bus from Bozen Bahnhof.

Rome2Rio.com is good for pinning down transportation options. It usually provides links to the appropriate bus line when a bus is involved.

Here's a web link to a website with a downloadable 2016 schedule for the buses. If I'm interpreting it correctly, there are a few buses going to Compatsch, in addition to the more frequent lifts.

Last year I was able to get a printed booklet containing the key schedules of tourist interest from the tourist office in either Bressanone or Bolzano. I think train, bus, and even lift schedules were included.

I haven't found the lift schedule, but I'm sure it's out there.

The #170 will get you to the bottom of the hill at the Cabinovia Alpe di Siusi. We made that mistake one year and had to lug our luggage up the hill. If you take the #170 to Vols/Fiè, you can change to the #2 bus which takes you to the upper piazza and closer to the lift. See here for a bus map of the area and here for even more info and schedules. Schedules are coordinated so when the 170 drops you off, the #2 should arrive in a couple of minutes.

Thanks everyone for your help! I think I've got it figured out now!