Hypatios’s name day is March 31, the feast of Hypatius, Bishop of Gangra.
Churches that follow the Old (Julian) Calendar keep the same feast on April 13 of the civil calendar. See everything commemorated on March 31.
The saint behind the name

Hypatius, Bishop of Gangra
March 31, Hierarch, Υπάτιος
St. Hypatius was Bishop of Gangra in Paphlagonia in the fourth century and a father of the First Ecumenical Council at Nicaea, where the divinity of Christ was confessed against Arius. A wonderworker famed for his prayers, he shepherded his flock with zeal against every heresy.
Also celebrating on March 31
These names share the feast, many of them other forms of the same name:
What to say on a name day
The Greek wish is Χρόνια Πολλά (Chronia Polla), “many years.” A call or a short message on the day is what people remember. See name day wishes you can send and what a name day is.