Juliet sent the Nurse at nine o'clock in the morning to meet with Romeo to find out the time and place when their marriage would be consummated. Juliet begins to panic because the Nurse doesn't return until 12:00 P.M.
In Act II Scene 5 Juliet becomes impatient with the Nurse since she set him at 9:00 A.M. when the clock sounded and she has been gone 3 hours. The Nurse is very talkative and was probably clacking like a hen with all her friends.
The Nurse left at nine o’clock and it is twelve by the time she returns (Act II, scene 5).