Finding source of Japanese 16.1'' naval gun's reload speed

in navweaps it said that usual reload speed of 24 seconds and at maximum 21.5 seconds
Searching on google I found ‘24 seconds’ based on Nordan Friedman’s ‘Naval Weapons of World War One’, but later 21.5 seconds… which source can prove it? Or just Navweaps got additional suspicious information from nowhere?

Navweapons lists its sources - why do you say they got the info “out of nowhere”?

Actually, I got direct source of those claims already. But thanks to your interest mate.