Not too shabby at all, for a good quality car model, detailed with good topo 20 hours is a good number, for one with no interior and minimal exterior detail like this, it would definitely be do able in under that, to put it in perspective this landrover model took 20 hours, and that was with no blueprints, just modelled by eye, and it has quite a lot of exterior details, like rivets, bolts etc, as well as some minimal details underneath, but you've definitely made a good start with this :D