For some, 14 days would be fairly easy.
For some, it would be a death march.
May depend on how well someone adjusts to the altitude.
Im planning to hike it in 2014 with my son if snow allows for an early enough start, but we will probably take a moderate pace for a couple of reasons:
1) dont want any injuries
2) since we will be flying on pre-purchased tickets, need a firm return date we KNOW we can make. See # 1
3) we kind of would like to enjoy it as much as possible.
Finishing a day later than planned, would cost $150 to change the tickets, and the incremental price for a next day ticket would likely be $300 each compared to 7 weeks in advance. It would cost me probably at least $750 to not show up on time.