Albert Barnes Commentary 2 Samuel 21:9

"And he delivered them into the hands of the Gibeonites, and they hanged them in the mountain before Jehovah, and they fell [all] seven together. And they were put to death in the days of harvest, in the first days, at the beginning of barley harvest." — 2 Samuel 21:9 (ASV)

In the first days - The barley harvest, which occurred around the middle or toward the end of April, was earlier than the wheat harvest (Exodus 9:31; Ruth 1:22).