Often it’s in the context of getting time in the game as opposed to sitting out on the bench and being impactful or contributing to the team when playing. “The rookie has been getting good minutes, scoring and playing good defense, when relieving the starter.”

"Good minutes" can mean two things: 1. Good quantity/number. Athletes always want to play in the game. In a 48-minute NBA game, a player would prefer 24 minutes on the floor instead of only 5 minutes. 2. Good quality. Athletes want to compete during the important parts of a game. If a player is only playing a few minutes at the END of a game when things are already decided, it's not very good competition. They may not be improving much. Those are low-quality minutes,

It means you were playing for several minutes and it was useful for you