My thought is this - I will start up the Roll20 game at 4pm. As with all good D&D adventures, it starts in a tavern. At 5pm, someone - or something - will burst into the tavern and set all those who are present on their merry way.

Players can use that hour to get used to the system and make sure all sound issues are resolved. They can mess about in the tavern, interacting with its staff and patrons, get to know their own character and each other's, and there may even be an easy tutorial battle or two to get into the swing of things.

The 4pm - 5pm section is optional, so come by 5pm at the latest but I can't really pause for everyone else if you have sound/tech issues.