As proved in the last World Cup, the ball is in play, in most games for between 55 to 75 minutes.
If you therefore take 65 as the average, if you stopped the clock every time the ball went out of play, a 7.45pm KO, would finish at about 10.05pm AND this doesn’t include stupid VAR
So in theory, by reducing the game time and stopping the clock, you would actually, increase the “ball in play” time.
PS——-I think VAR is going to spoil the game, for live game audiences !!!!! It’s a thing for plastic armchair watchers