It probably won't shorten game time at all. Any time saved by not making a pitching change will be offset by a pitcher afraid to throw strikes to a guy he doesn't feel he can get out, and/or shenanigans teams will apply to get around the rule. And any rule that favors the offense does not cut time out of the game. It's just such a pointlessly dumb rule. i don't even know that game duration is the issue, so much as big gaps of time where nothing horsefeathering happens and you gotta sit there and watch Bruce Bochy or whoever do their interminable waddle to the pitchers mound followed by eighteen meaningless warmup tosses before the same exercise gets repeated in two minutes after the new guy issues a walk it's the worst part of baseball and nobody likes it