For those wondering, here is the definition cleaningtheglass.com uses for garbage time:
The exact definition CTG uses is: the game has to be in the 4th quarter, the score differential has to be >= 25 for minutes 12-9, >= 20 for minutes 9-6, and >= 10 for the remainder of the quarter. Additionally, there have to be two or fewer starters on the floor combined between the two teams.
Importantly, the game can never go back to being non-garbage time, or this clock resets. For example, if it's a 30 point game to start the 4th quarter, but one team comes back and pulls the game within 8, that comeback is not counted as garbage time. If the leading team regains control and expands the lead back out, garbage time would start when the score went back above 10.
This might not capture all of what we'd call garbage time, but it seeems important to err on the side of caution and not mistakenly filter out any game time that we would not consider garbage time.