To activate and de-activate garbage time, on coding side, if game-code has been written properly, it may be some minutes of code changing. Its almost nothing in case of time and it would be a great update.
Also, i want to add to the above, that sometimes even training can be completly destroyed if you add a player in the line up. You have to play with 1 C for example, if you add a 2nd one with no playing time, he may get garbage time and destroy the training of the first one, but if you do not add him in the line up, your first Center may get injured and then play the whole game with no other Center.
Garbage time is just a garbage feature as long as no one takes control of it.