Don't try to play one game with six players. It doesn't work, for the exact spotlight-time problems you're concerned about. Five is doable, but be prepared for it to be an incomplete introduction to the game.
Microscope is a wonderful game, but it does not scale up past five players very well at all. I have a hard time introducing the game to new people even with only five players — new players means slower turns, and more people means longer between turns — and it usually only results in one Focus being completed in an evening, and sometimes not even that. Partly this is because I take the game's advice to make Scenes early and often (I find that getting fewer history turns but more Scenes makes for a better introduction to the game than more turns and fewer Scenes).
For your group especially, jumping straight into a Scene during the very first player's turn (you, probably, if you're following the teaching-the-game advice in the back) is the best way to get right into the roleplaying that they're expecting to be learning about tonight.
I've found that the ideal for new groups is 3–4 players. Five is doable, but expect to get much less history made than you'd expect (or more history, but not much roleplaying of characters) unless you have in excess of three hours.
Split a large group into separate games
If you find yourself with a group that's six or larger, divide into smaller groups. Have the group you're in be the "demo" group, and have the other group(s) players watch the first group play through the setup and the first history creation by the first Lens. Then pause the first group and help the other group(s) get started for a few minutes. Now that everyone has seen how the game starts, everyone is able to start a game and you don't need to facilitate as much.
Be ready to leave your game for a few minutes when other games get to playing a Scene to help facilitate that for the first time, too. Since often a game can roll just fine without the facilitator once the idea of making history is understood, you'll have a bit of time to drop out and return without disturbing the flow of your game or them missing your facilitation at all, or much.