So we played for about 3 hours last night and pulled off two encounters. It was a six man group in a made for 4 adventure but with some adjustments and some on the fly additions (stealthed goblins in a back room) I was able to make it fairly challenging for them.
I think I had some good flow and everyone embraced the RP element too which was fun to watch - especially as they stressed about what could be behind a locked door.
Overall it seemed to be a success and everyone was asking when the next session would be.