Exodus 9:32

Wheat. In Egypt the wheat harvest began about a month later than the barley harvest, and continued until the early part of April.

Rye. Rye was not grown in Egypt, and it is generally agreed that the Hebrew word here translated “rye” was in reality spelt, an inferior kind of wheat now ordinarily raised in Egypt as an aftercrop. As the monuments show, it was grown more commonly in ancient times than it is today. Being sown simultaneously with wheat, it would also ripen about the same time, in late March.

The remark that the flax and barley had been destroyed, but that the wheat and spelt had escaped major harm, shows that the plague of hail must have occurred at either the end of January or the beginning of February. That would be two or three months before the Exodus. On the duration of the plagues, see on chs. 7:25 and 9:31.