to me, minor things like this are what you do once your regular routine has become easy. So lets say you shadow box for 10 minutes everyday, eventually the body adapts and we must intensify the workout. If you just keep adding time to your workouts, youll end up at the gym for 4 hours. So instead of now shadowboxing for 20 minutes everyday instead of 10, you need to find a way to maximize that 10 minutes.
A example i have done myself for this is instead of resting in between rounds, doing burpees etc instead.