After reading @jkerian's comment in this post, I started thinking about this. Here's the comment in full:
On a side note, all days ending in '4' are also irregular, and use ~よっか. So the 14th is じゅうよっか, the 24th is にじゅうよっか, even though all the other days >10 switch over to ~にち
Obviously the most calendar days is 31, but does this rule apply if I want to refer to the 34th day? Or 84? Or any number of day that ends in 4? Or twenty (
はつか - ２０日)? Or do these rules only apply to so-called "calendar" speak?
I realize there are probably better ways of saying such things, but here are some examples:
- 事故から４４日目 → The 44th day since the accident. （よんじゅうよっかめ or よんじゅうよ（ん）にちめ?）
- 裁判長は犯人に120日間の懲役を申し渡した。 → The judge sentenced the criminal to 120 days in prison. (ひゃくはつかかん or ひゃくにじゅうにちかん?)
- 宇宙探査機が2374日間で往復した。 → The spacecraft made its round-trip in 2374 days. (にせんさんびゃくななじゅうよっかかん or にせんさんびゃくななじゅうよ（ん）にちかん?）