Have its/(one's) day verb phrase
The antonym of this phrase is "have had its/one's day", which means "to be much less popular than before".
If someone "has his/her day" or something "has its day", it means that someone reaches the top of his/her success, or something is at the peak of its prosperity.
If you are diligent and persistent enough, you will have your day sooner or later
His business eventually has its day thanks to his excellent leadership and management skills.
Everybody knows that Apple is having its day.
The verb "have" should be conjugated according to its tense.