1.
twenty days
A period of twenty days.
二十日かかった。
It took twenty days.
二十日ぐらいかかる。
It takes about twenty days.
二十日間休みを取った。
I took twenty days off.
工事は二十日で終わる予定です。
The construction is scheduled to be completed in twenty days.
薬を二十日分もらったので、来月まで足りるはずだ。
I received twenty days' worth of medicine, so it should last until next month.
2.
twentieth day of the month
The twentieth day of any month.
一月二十日
January 20th.
二十日に届きます。
It will arrive on the 20th.
二十日までにお届けします。
We will deliver it by the 20th.
来月の二十日に会議がある。
There is a meeting on the 20th of next month.
二十日は祝日なので、学校も会社も休みです。
The 20th is a holiday, so both school and work are off.
二十日 has two uses: "twenty days" (a duration) and "the 20th" (a date). The reading はつか is irregular and must be memorized.
SPECIAL DAY READINGS (1st-10th):
Days 1-10 of the month all have unique native Japanese readings: 一日, 二日, 三日, 四日, 五日, 六日, 七日, 八日, 九日, 十日.
AFTER THE 10TH:
Most days use Sino-Japanese numbers + 日 (e.g., 十一日), but a few retain special readings:
- 十四日 (14th)
- 二十日 (20th)
- 二十四日 (24th)
COMMON COMPOUND:
- 二十日大根: small Japanese radish (literally "20-day radish" because it matures quickly)