This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. Note that the 日 reading is the alternate reading, じつ.
Thank you so much for the other day.
I heard that the festival I went to the other day in Hokkaido is held for twenty days.
She was lying about being sick in bed for a few days.