Citing Deut 16:9-12 and the Gezer Calendar, K. Lawson Younger says in NIV Application commentary on Ruth, “the time period from the beginning of the barley harvest to the end of the wheat harvest was normally seven weeks, concluding at Pentecost.” Presumably, this was the festival that Boaz was celebrating in Ruth 3.

Booths begins after the gathering of the wine (Deut 16:13), but Pentecost is the feast of wheat. Pentecost is also the festival of the law, and this gives an additional layer to Ruth’s approach to Boaz. Pentecost celebrated the time when Yahweh spread His wing over Israel at Sinai (cf. Ezek 15), which is what Boaz does for Ruth.