A one-day modernization of the 1939 Royal Navy

Would Britain trade one day at the start of the Second World War to modernize every Royal Navy ship to the best 1939 standard?

Yes; the fleet-wide gains in engines, radar, armor, and anti-aircraft weapons would far outweigh losing one day.

Britain would accept the lost day without hesitation because the ships could use dry docks across the empire and retain their global distribution. Germany could accomplish little at sea during the brief pause, while Britain would recover a uniformly modern fleet. The imagined refits add current engines, radar, armor improvements, and anti-aircraft weapons, with Queen Elizabeth- and Renown-style rebuilds illustrating the scale of the gain. Modernizing the Royal Navy's many older C-, D-, and E-class cruisers at once could matter even more than the battleship work.