People have often asked me, how long did the plagues last? Well, since no one alive today was living then we can't be for sure but we do have some pretty good clues to follow.
The Mishnah says the plagues lasted for one year, but the one year began from the “burning bush” incident until the Exodus. (Eduyos 2:10)
Rashi says that each plague lasted one month - 3 weeks for a warning, and one week for the plague itself after it hit; hence the plagues lasted 10 months.
What the Bible Has To Say
The 1st plague lasted for 7 days (Exodus 7:25)
The 9th plague lasted for 3 days only (Exodus 10:21-23)
The 10th plague lasted only one night (the night of the Exodus (15th of the first month)
That is just 11 days for 3 of the plagues.
Let us now consider the 7th plague. In Exodus 9:31-32 we read, "the flax and barley were ruined, for the barley was in the ear and the flax was in bloom. But the wheat and the spelt were not ruined, for they were not ripe”. Flax blooms in February/March and it says the barley had green heads, the Hebrew word says it means it was aviv. Barley also blooms around February; here it says it already is a young, tender ripened plant, so they were both ruined. We know that wheat and spelt bloom a month or two later (ripe at Shavuot) that is why it states that they were not ruined, so hence this plague could not have lasted more than a month, and really not that long, because the barley was aviv (ripe) and when the barley was aviv, God said that was the first month, and the Passover took place in the first month. So, all of the 7th plague took place in the first month of aviv.
When the 8th plague was sent (swarms of locusts), God said they would destroy "every plant of the land that the hail left." (Ex 10:12). This means that it shortly followed the hail, still before the wheat and spelt were in bloom (probably in late February or early March). We know the 10th plague occurred on the 15th of Aviv. Therefore, the time frame for the 7th plague through the 10th plague was almost certainly no more than one or at the most two months, and probably less, since we know barley is aviv for Passover, and the beginning of months is when the barley is seen to be aviv.
Consider, the 8th plague of locust. We know that from even modern sources that locusts can devastate entire vegetation in just 2-3 days. They definitely don’t need a whole week. Historically, they usually go thru an area and wipe it clean in a couple days and they are moving on to the next area.
So, you would have 4 plagues being completed in, let’s say, 2 months. We should be very safe in saying that.
This works out to about 2 weeks for each plague, from the warning to the actual completion of the plague. If we carry this out to the other 6 plagues, we get 12 weeks. So, the total is 20 weeks (8+ 12=20), or could be about 5 months for all 10 plagues.
This being said, if we make the average length of each plague approximately 4 days, we would have a total of 40 days that the plagues themselves lasted. Well, we know what the number 40 represents in the Bible. Testing/trial/or punishment, for the purpose of making perfect. This number is throughout the Bible. Moses had 40 years preparing to go back to Egypt, 40 years of wandering in the desert (Num 14:33-34, 32:13), 40 days of rain for Noah's flood (Gen 7:4,12), Goliath tormented Israel for 40 days before God helped David kill him (1 Sam 17:16), God gave Nineveh 40 days to repent or be destroyed (Jonah 3:4), Yeshua was tested for 40 days, etc.Ex 9:31 So, this scenario would fit quite well in the Biblical pattern.
Of course, we don’t know for sure. I personally believe the Creator did a quick work with the plagues.