In the Old Testament times the night was divided into three parts of four hours each, called watches.

The first of these watches is mentioned in Lamentations 2:19.

Lam 2:19  “Arise, cry out in the night, At the beginning of the watches; Pour out your heart like water before the face of the Lord. Lift your hands toward Him For the life of your young children, Who faint from hunger at the head of every street.”

The middle watch is mentioned in Judges 7:19.

Jdg 7:19  So Gideon and the hundred men who were with him came to the outpost of the camp at the beginning of the middle watch, just as they had posted the watch; and they blew the trumpets and broke the pitchers that were in their hands.

The last watch, also called the morning watch, is mentioned in Exodus 14:24.

Exo 14:24  Now it came to pass, in the morning watch, that the LORD looked down upon the army of the Egyptians through the pillar of fire and cloud, and He troubled the army of the Egyptians.

By the time of the New Testament, a fourth watch had been added (presumably as a result of Roman influence) so that the night was divided into four watches of three hours each: 6pm – 9pm, 9pm – midnight, midnight – 3am, and 3am – 6am.  They seem to have been called the first watch, the second watch, the third watch, and the fourth watch.  The third and fourth watches are mentioned directly.

Mat 14:25  Now in the fourth watch of the night Jesus went to them, walking on the sea.

Mar 6:48  Then He saw them straining at rowing, for the wind was against them. Now about the fourth watch of the night He came to them, walking on the sea, and would have passed them by.

Luk 12:38  And if he should come in the second watch, or come in the third watch, and find them so, blessed are those servants.

When Jesus spoke of His return He said:

Mar 13:34  It is like a man going to a far country, who left his house and gave authority to his servants, and to each his work, and commanded the doorkeeper to watch.
Mar 13:35  Watch therefore, for you do not know when the master of the house is coming—in the evening, at midnight, at the crowing of the rooster, or in the morning—
Mar 13:36  lest, coming suddenly, he find you sleeping.

In mentioning four time periods, “in the evening, at midnight, at the crowing of the rooster, or in the morning”, it is quite possible that Jesus was alluding to the four watches of the night.