8/6 was the date that Prince had the injury, debuted November 20th against the eagles. So lets do some math here...
104 days from the surgery date (8/8 i'm pretty sure). So 104/7= 14.857142857142857~15 weeks. Now Prince was actually almost put on the roster for the game the week previous, but knowing that he wasn't adept with the terminology and defense he was not. So there is a case that the rehab would actually be 14 weeks.
The opener on september 5th will be a total of 110 days (~16 weeks) from today (Hakeem's surgery date). So I am not saying that Hakeem will be back, but given previous players with this injury, he will be able to play around that time. Also, there is a possibility that Hakeem could be back even earlier because of that 1 week that Prince wasn't put in the lineup but almost was, and also because he might get better blood supply to the area.
Beatty had a similar injury but he was only out for 2 months.
Regarding the statement that Nicks's production decreasing due to not playing , I feel like this won't really be the same. He clearly has chemistry with Eli and knows the system well. I am kindof actually happy because now this won't give him the chance of putting stress on his body in camp and although he'll have to adjust, being a guy who frequently gets dinged up this means he might last longer without injury during the season.
Also there's this:
One person familiar with WR Hakeem Nicks' fractured foot said it was more like a "4- to 6-week" injury. Opener vs Dallas still in play.