You say you want the shortest amount of time but have you studied enough for the required oral exams, you will need to be very familiar with the FAR/AIM, license and maintenance requirements, airspace, charts etc etc etc, you need to know the oral exam guides cover to cover and more!
The written exams are piece of cake but if you havn't studied for the oral exams you wont even make it into the aircraft!
Don't forget as well all the extra things in the FAA CPL test that you might not have done, chandelles, lazy eights, eights on pylons, steep spirals, power off 180's etc, all of this may be why they are quoting you more hours.