ESV - 20 Moses and Aaron did as the Lord commanded. In the sight of Pharaoh and in the sight of his servants he lifted up the staff and struck the water in the Nile, and all the water in the Nile turned into blood.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Is the question wanting to know the period of time that elapsed between the beginning of the plagues in Exodus 7 and the final plague that killed the Egyptian first-born in Exodus 12 (which I attempted to address in my response), or the date in secular history when the plagues occurred?
The reason I asked this question is because in Exodus 9 we read about "The Plague on Livestock". All the livestock was killed. In Exodus 14 we read 7 He took six hundred of the best chariots, along with all the other chariots of Egypt, with officers over all of them. 8 The Lord hardened the heart of Pharaoh king of Egypt, so that he pursued the Israelites, who were marching out boldly. 9 The Egyptians—all Pharaoh’s horses and chariots, horsemen[a] and troops—pursued the Israelites and overtook them as they camped by the sea near Pi Hahiroth, opposite Baal Zephon. Where did Pharaoh get all the horses in such a short period of time?
I can think of three possible explanations (although there might be others that do not occur to me).
Although Exodus 9:3 mentions a plague that would be brought upon "cattle which are in the field, the horses, the asses, the camels, the herds, and the flocks", Exodus 9:6 mentions only cattle being afflicted. If this reference to "cattle" encompassed only bovines (which I think would be the common construction), and did not include other types of animals, perhaps the Egyptian horses were somehow spared at that time.
Alternatively, perhaps "which are in the field" is the operative phrase, indicating that animals that were in shelters were spared, as occurred in Exodus 9:20-21, when the cattle that were brought into structures were saved from the plague of hail.
A third possibility might be that the horses designated for use by Pharaoh and his army received more attention or greater care than "common" horses, and would not have fallen under the heading of horses "in the field", or been subject to the plague, and would therefore still have been available for Pharaoh's use in pursuing the Israelites.
Has any thought been given to the fact that if all the Egyptian animals were killed (7th plague), then, for the firstborn of the Egyptians animals (and people) to be killed (12th plague - Passover) then there would have needed to be several months or years for the Egyptians animals to be replenished before the Passover.
The plague of hail did not kill all the animals, just the ones left outside.
"Give an order now to bring your livestock and everything you have in the field to a place of shelter, because the hail will fall on every person and animal that has not been brought in and is still out in the field, and they will die.’ Those officials of Pharaoh who feared the word of the Lord hurried to bring their slaves and their livestock inside. But those who ignored the word of the Lord left their slaves and livestock in the field." Ex 9:18-20
As for Ex 9:6 dealing with the plague on livestock, the 'all' in Hebrew doesn't imply every last animal, but rather a very great number - it's a bit lost in translation.