You can have multiple people defending a single car. There are guild perks that allow a guild to have more defenders per car.
Guild with the most points when the war ends wins.
Matchmaking happens for everyone at the same time. Guilds can queue for the next war while they’re in the battle phase, and then matchmaking happens at 11 AM CT the next day.
So it goes like this:
Matchmaking at 11 AM
Sabotage Phase Begins
Return to day 1 and repeat.