Teams are free to create and are designed to ensure that you and your mates all get assigned to the same start time. HOWEVER, you will ONLY be running together if everyone is registered for the same team in the same starting wave. This means that if the wave your team has registered for sells out before all your team members register, they will NOT be in the same start time as you. Teams can consist of 1-100+ participants – there is no maximum or minimum amount of people who can be on the team.
If you want to run at the same time as your friends, you will need to create and join the same team.