The QF 767 fleet is 'slow flying' at the moment (sharing the hours around all airframes) and last I heard was about 8 1/2 hours per airframe. 9 hours isn't enough. 11 would be satisfactory. Closer to 12 would be the norm for an efficient user. Given the schedules and time zones, I think you'd struggle to get four crossings out of a 737 per day. If you did you'd still only touch on about 12 hours. If you not get 3 crossings then hous are 9-10 and you're struggling.