Twentieth Day, Day Twenty, Twenty Days
noun
Two times ten days is twenty days.
はつか
Words that count days use an exceptional reading. The readings for 二十 are exceptions, and 日 takes the kun'yomi reading. Here's a mnemonic to help with that: If you make one hat for twenty days you'll have enough hats (はつ) to fill up your car (か) completely! That's a lot of days and a lot of hats.
二十日にテストがあります。
There is a test on the twentieth.
あと二十日で２０１９年です。
It will be 2019 in twenty days.
二十日にボーナスが出ます。
I will get a bonus on the 20th.