LateFinals, do you have a reference for the 24 hours thing?
Not doubting what you've been told at all - different Forces have been known to interpret the requirement differently - it's just that
the GAR Form still clearly refers to 12 hours and the
web submission form for my local force does likewise.
The quote from the GAR Form is:
AT A GAA AIRFIELD YOU CAN FLY TO AND FROM ANYWHERE, BUT THERE ARE DIFFERING PERIODS OF PRIOR NOTIFICATION REQUIRED DEPENDING ON YOUR
DESTINATION/DEPARTURE POINT.
OUTWARDS – TO ANOTHER EU COUNTRY THERE IS NO OBLIGATION TO ADVISE
CUSTOMS OF YOUR DEPARTURE.
OUTWARDS – TO A NON EU COUNTRY (INC CHANNEL ISLANDS*) YOU MUST NOTIFY
CUSTOMS AT LEAST 24 HOURS PRIOR TO DEPARTURE.
INWARDS – FROM ANOTHER EU COUNTRY – 4 HOURS PRIOR TO ARRIVAL
INWARDS – FROM A NON EU COUNTRY – 24 HOURS PRIOR TO ARRIVAL
*CHANNEL ISLANDS – NOTIFICATION PERIOD IS 12 HOURS.