The old blue cover BW 'Inland Cruising Booklets' has 'Code of conduct - For the Guidance of Pleasure-craft Users'.
Para6: "Mooring places are suggested, where possible, in the Inland Cruising Booklets, and for reasons of safety these should be used in preference to locations chosen at random.If mit is not possible to reach a proper mooring, a spot should be chosen where obstruction is unlikely to be caused. On certain waterways a vessel moored at night must exhibit, where it can best be seen, a white light of such a character as to be visible all round".
No mention at all of any mooring time limits, and I certainly do not remember any in the late 50s.