How long did a train ride take for a passenger from Zürich HB to Milano Centrale in the 1920s? Let's assume that it's a typical train with a typical engine at that time which doesn't stop for loading/unloading passengers (but it stops if necessary to reload fuel), and it doesn't have to wait for other trains, it takes the fastest route, and it doesn't take risks to go faster than typical express passenger trains of that time.
The Gotthard Tunnel was opened for traffic in 1882, and the Simplon Tunnel was opened in 1906, so the train can use any of these to cross the Alps.
As of today, a typical, scheduled ride takes 4 hours and 3 minutes, which sounds a bit slow, because the distance between the two cities is less than 300 km, and trains now can go now faster than 100 km/h on average. Is there any reason why a 4-hour ride (with the special conditions above) wouldn't have been possible in the 1920s?