sephardi mizrachi eastern - Why was the Shulchan Aruch's ruling to wait until Lad LaOmer to cut one's hair?

The Shulchan Aruch (493:2) writes that one should not cut one's hair until the morning of the 34th day of the 'Omer ("אין להסתפר עד יום ל"ד בבקר"). What is the source for waiting until the morning of the 34th day?

Answer

The Beit Yosef there quotes many Rishonim who have a version of the story (Yevamot 62b) that Rabbi Akiva's students died until פרוס העצרת a half [month] before Shavuot. So 49-15=34 and on the last day we say that a partial day counts as the whole day so on the 34th in the morning, the mourning ends.