Thursday, then Wednesday.
Her express purpose is to make the wedding arrangements. While she is about it, she warns Romeo not to mistreat Juliet.
It was moved forward a day (from Thursday morning to Wednesday morning). This meant that the Friar had to rely on a letter to tell Romeo of Juliet's fake death.
Actually all the arrangements for their wedding are made through the Nurse and Friar Lawrence, so Romeo cannot tell Juliet anything of the kind. The nurse makes the suggestion that Juliet should get permission to go to confession so she can get to the church on time.
Monday
On the day of Juliet's wedding to Paris, she takes a potion given to her by Friar Laurence to make her appear dead and avoid the marriage. When her family finds her seemingly lifeless, they grieve and lay her in the family tomb.
In the afternoon. In Act II Scene 4 Romeo says "Bid her devise some means to come to shrift this afternoon; and there she shall at Friar Lawrence's cell be shrived and married."
Friar Lawrence organises for Friar John to bring Romeo news of Friar Lawrence and Juliets plan (Act Five, Scene 1)
The Nurse provided the rope ladder for Romeo to climb up to Juliet's room on their wedding night and she served as a messanger for Juliet. She was one of the few adults in on the secret, along with Friar Lawrence, and since women Juliet's age weren't allowed out of the house often, the Nurse sent messages between Romeo and Juliet. The Nurse also raised Juliet since she was an infant, and even breastfed her. She was more of a mother to her than Lady Capulet.
Romeo.
Romeo "Is the day so young?"
Juliet's marriage was arrnged for Thursday after Capulet changed his desicion.
Romeo speaks first saying "Is the day so young?"(1:1 152)