Important Note: Once exposed, process PAN F Plus as soon as practical – we recommend within 3 months. This is the Ilford statement on page 1 of its leaflet about Pan F so it looks to be more than a matter of days
Sooner is better, regardless. Three months would be an absolute maximum.
Sadly, I have been bitten by the problem and have learned quite a lot about it. I have a bunch of 2006-expired 35mm Pan-F Plus that I've been using up since I acquired it in early 2007. I've kept it frozen at about -18 C so when used properly, the results have been excellent despite the age.
I got out of darkroom work for awhile and unknowingly forgot exposed two rolls of Pan-F Plus, one in the darkroom and one in my freezer. The one that was frozen turned out well, with no obvious loss of shadow detail. The one that was left at room temperature essentially disappeared! No edge markings. Really faint traces of image density on a few of the frames, but most were simply invisible. I know the processing was okay because it was the bottom roll in the tank of seven I processed simultaneously (which all turned out fine; some shot only week before last) and the leader was black, as expected. I expected loss of image density, but did not expect to lose the edge markings.
I think you can probably keep exposed Pan-F Plus for a long time - if you freeze it. I would need to conduct some experiments to see if there might be some loss of image density, but it would take a few years to know the answer.

While I will try to avoid delaying in the future, for my purposes, frozen exposed Pan-F Plus is stable enough for me if I can't get to the darkroom for a few months for some reason.