I followed the instruction by beep88 and noticed something important.

The info regarding the open hours provided in English misses a thing. ゆうゆう窓口 or yu-yu madoguchi. It’s the after-hours counter for pick-up.

For example, at Yokohama central post office, English website says, on holidays they are open until 1900 but it doesn’t mention yu-yu madoguchi, but Japanese version says its yu-yu madoguchi is open 24 hours.

This may have something to do with human resource late night. Maybe better have Google translate handy.