I may have missed something here. Where does it say that Pan F has to be developed promptly? I don't recall seeing any direct specialist instructions issued by Ilford to the effect that is must be developed sooner than other films.
It says that on most film packs to develop promptly but that is an open argument with no time element, but to be quite honest I have never bothered with it in the 50 odd years I have been involved with photography. Being a slow emulsion, Ilford Pan F is probably more stable than say Tri X or HP5. Less susceptible to ambient temperiture fluctuations and any exterior radiation that may affect all film after a while.
I have often used Pan F both the old and the newer Pan F plus and not been able to develop them for several days if not weeks when I am away. I personally feel that this develop 'promptly issue is largely an urban myth.