Do I need to create a team post-registration?

The only way to guarantee that you receive the same start time window as your teammates is for all members of your group to book the same 1 hour start time window.

Team creation will not impact your start time window. 

Participants with different start time windows on the same team will not receive the same start time. If members of your team currently have a different start time, they can change their start time via MyEvents based on availability.

Instructions on how to make changes to your start time can be found here.