Games would finish about 5 hours later.,
I'm sure I read somewhere that in 45 mins the ball is in play about 25
But I don't think it would, Pete, for the very simple fact that players would see they are not getting away with it.
We all scratch our heads with refs sometimes thinking '5 minutes added on? What the hell!' and then the flip, 'Only 5 minutes added on, you're having a laugh ref.' It's not at all an exact science and quite often you will have Clive Eakin declaring his surprise at the amount of time added, or not added on.
If the ref controls a timer on the scoreboard we would all see exactly where he has stopped it and he would be under scrutiny for all to see if he wasn't stopping his watch. And if he was stopping it, for how long.
Pointless the goalkeeper wasting time if he can see the clock not moving. Same too for subs and throw ins and free kicks etc. The ref kills the game until the ball is back in play, making time wasting a pointless exercise. Time wasting wouldn't work.
Added to that of course there would indeed be some time wasting to try and kill momentum, at first at least. One side on the up, with the momentum, other side tries to kill that momentum by taking their time. That's where the ref would then book them. The clock has stopped, but they are still trying to time waste.
Bottom line is, if teams see there is no advantage whatsoever in their wasting time they wouldn't do it and there is no way a match would go on for the time you have described.
Clock stops. Any time wasting then while the clock is stopped results in cards.