Currently 4:20, 5:00, 5:40...these are listed 20 minutes, maybe less at that hour. Since you are flying inside Schengen you can likely get away with the 5:00 AM bus unless you have major issues to deal with regarding your bags and going through security. Since we are carry-on only, planning the 9:20 for our 12:15 flight to the US a few days after your trip. Since you are staying near there, get your tickets ahead of time.
And whatever you do, do NOT make the boneheaded mistake I made a few years back, seeing the Aeroporto bus at the appropriate time and getting on, not realizing it was going to Treviso. Luckily I noticed our stopping at the station in Mestre, knew this was wrong, and heard someone as they boarded ask the driver "Treviso". And luckily we could get out and catch a bus from there shortly, using our same ticket. Could have been a really costly error as we were flying home connecting in Frankfurt!