Just checked it again, it seems like it's possible to rescue Vehlis after the first scene.
On the first day visit every location, starting with the castle and ask around. Scan the castle and talk to Alioch and discuss everything.
Rest.
Second day go to the castle, investigate Jasmine's room. Then go to the market and buy the potion. Discuss things with Amelia. Talk to Alioch and i was already able to go and save Vehlis.
I think you can watch up to 4 scenes and still succeed if you want to or if you need to do so for some reason.