Difference between "à quelle heure" and "pour quelle heure"

Question

Is there a difference between these two phrases:

On part pour quelle heure ?

and

On part à quelle heure ?

Can I use à instead of pour?

Answer 1

The usual sentence is On part à quelle heure ?

If someone asks me On part pour quelle heure ? I might understand that it is not about the time we have to leave the place we are, but the time we have to be at another place. Assuming there is a train every hour and the station is 20 minutes away, On part pour 8 h would mean that we have to leave at worst at 7:40 but actually earlier so as not to miss it.