From the PDF: Adventure Overview
The Master’s Vault is a 5th Edition adventure for four to six 1st level characters from Roll20.
At the end of the adventure, the characters should level up to 2nd level. The adventure is
meant to teach the basics of 5th Edition and Roll20 to new players, but veteran gamers will
still have fun diving into The Master’s Vault. I've not played it, but from what I can tell, there are about 5-6 encounter locations. While you could probably run the whole thing in a single session, it's probably more reasonable to expect between 3-6 sessions based on how new your players are, how new you are, how fast you like to go, how long your sessions are, and how much you embellish. I think there might be a video of them running this during Roll20CON, but I'm not certain.