20th day of the month
Refers specifically to the 20th day of a month. The reading はつか is irregular and must be memorized.
会議は来月の二十日です。
The meeting is on the 20th of next month.
二十日までにレポートを提出してください。
Please submit the report by the 20th.
20 days
Indicates a duration of twenty days. The reading にじゅうにち is also possible but less common; はつか is the standard reading for this meaning as well.
この薬を二十日間飲み続けてください。
Please continue taking this medicine for 20 days.
二十日も雨が降り続いている。
It has been raining for 20 days straight.
There is a meeting on the 20th of this month.
It took twenty days to finish this construction work.
It rained for the first time in twenty days.
Uncommon variant using the kanji 〇 for zero.
Archaic kanji form; rarely used in modern Japanese.