Jesus says (Matthew 16:21) that he will "be raised again the third day." Hence, in Jewish usage {the third day} must mean the same as {three days and three nights}. It was and is customary with the Orientals to make any part of the day stand for the whole twenty-four hours. Compare 

Matthew 16:21
From that time forth began Jesus to shew unto his disciples, how that he must go unto Jerusalem, and suffer many things of the elders and chief priests and scribes, and be killed, and be raised again the third day.

Mark 8:31
And he began to teach them, that the Son of man must suffer many things, and be rejected of the elders, and of the chief priests, and scribes, and be killed, and after three days rise again.

Matthew 27:63-64
63 Saying, Sir, we remember that that deceiver said, while he was yet alive, After three days I will rise again.
64 Command therefore that the sepulchre be made sure until the third day, lest his disciples come by night, and steal him away, and say unto the people, He is risen from the dead: so the last error shall be worse than the first.