moa999, I disagree with 6 hours for the 737, it is somewhere between 7:00 & 7:30 hours per day on the numbers I have seen. And still there looks like being a net increase of 7x 737 aircraft this year. Retirements of the 767 need to be considered, how this affects the average remains to be seen.
Where exactly are the 737s sitting outside of 9-5.
You have made an assumption that they are doing straight (0:35) turnarounds - that isn't the case, except in limited space apron / high frequency outports (KTA,PHE,BRM etc). They tend to do longer turns, particularly during the middle of the day. The net result is two departure peaks, early morning and late afternoon / early evening.