Family of 3 with young child going in a few weeks from Salta to Tupiza...
we will be aiming for 3:30 train Villazon to Tupiza
how much time should be expect to spend waiting for visa at border crossing. Should we get expedited visas in USA?
Family of 3 with young child going in a few weeks from Salta to Tupiza...
we will be aiming for 3:30 train Villazon to Tupiza
how much time should be expect to spend waiting for visa at border crossing. Should we get expedited visas in USA?

I've never crossed at Villazón. But, I don't think it would take more than 30 minutes at the border assuming you have everything ready.
Don't get expedited visas in the States. You're begging for trouble in the form of extra requirements and/or not getting your passport back in enough time for your trip.