How to prevent 45 minute games.

If you're winning* and have taken mid inhibitor, DO NOT go down mid lane again until you need to (inhibitor respawns). Super creeps will automatically push and pressure that lane for you and you or your teammates do not need to be there. I've seen low elo waste countless minutes wondering around in the enemy base doing absolutely nothing when they push mid even though inhibitor is down.

Group into another lane, pressure dragon, baron, but do not go down mid lane and fight pointlessly in their base. You give your enemies a large chance to come back if you die and your enemies are allowed to just farm a downed inhibitor instead of being punished for it.