In my experience it takes between 2 to 3 hours to fully charge a car battery using the highest amp setting on the car battery charger.
If you charge the car battery using the trickle charge option it could take 8 hours.
But on the highest charging setting it should take only 2 or 3 hours to give the battery enough charge to start the vehicle up.
Then the battery should charge up some more with the alternator as you drive the vehicle down the road.
If the battery is really low then it might take 8 hours of charging to fully charge the battery but you should be able to charge the battery up enough within 2 or 3 hours and the vehicle should start.