Think of the Garage pick as your bench.
You must select your Garage driver at least five minutes before the official start time of the Race, but you can substitute your Garage driver for a driver in the starting roster an unlimited number of times, if desired, until the start of the final stage while the Race is in progress. If the final stage begins early due to NASCAR’s new caution procedure, the garage will remain open until the lap on which the final stage was originally scheduled to begin.
The combined race points of the drivers that finish the Race in the Team’s five active starting roster slots will count toward the Team’s final score for that week.
More information about the Garage pick can be found in the Official Rules page.