I finally got about 75% better after about 6-8 months - I could walk normally, with pain after about 20 minutes, but couldn't work out at all (power walking was a killer on the feet). So, I started using an exercise bike at the gym, with no resistance, just really spinning the wheels - and after a few weeks, my feet became as inflammed as ever. And, 16 months later, I am still miserable - I use a wheelchair to go anywhere I have to stand over 5 minutes. I sit on a chair to brush my teeth, I kneel on a chair in the kitchen. I am very disabled. And, if I had paid attention to my feet in the first place, this wouldn't have happened.
I know, as a former runner, that it is really hard to lay off it - but, my best advice is to stop running NOW, forget this marathon (there are others later), and let those feet heal. My husb, an avid runner with several marathons under his belt, got PF 10 years or so ago - he stopped running immediately, waited 1 month, took PT, did stretches, and was fully cured. He continues to run pain-free today. Too bad his idiot wife is crippled.
I hope you will consider what I am saying - I know its not what you want to hear. I was just told Friday by my DPM that he doesn't think I will ever recover, since I have had this so long. Best wishes