Exodus 7:25 tells us that the first plague with the water being turned into blood lasted 7 days.

Exodus 10:21-23 tells us the 9th plague (darkness) lasted for 3 days.

Exodus 11:4-10, 12:29-30 tells us the 10th plague of the firstborn of man and beast being killed happened overnight on the Eve of the Passover.  As for the rest of the plagues, the Bible does not say how long they lasted.