The entire play occurs over the course of four days. Shakespeare's source for the play is Arthur Brooke's "The Tragicall Historye of Romeus and Juliet" which takes place over nine months. The fact that Shakespeare condenses it down to four days is amazing.
The play begins on a Sunday, and on that day the reader is introduced to a lovesick Romeo who is lamenting that he can never be with the beautiful Rosaline. From there Romeo meets Juliet, falls madly in love, and goes through the whole balcony scene.
Monday rolls around and Romeo and Juliet get married and spend that night together. Capulet agrees to let Paris marry his daughter that Wednesday, which Paris thinks is too soon, so he says Thursday should be good.
Monday! ha, ha! Well, Wednesday is too soon.
Thursday let it be—a Thursday, tell her
She shall be married to this noble earl.
That takes you through Act 3. The remaining two acts go like this. Tuesday Juliet gets the poison. She's found dead on Wednesday morning and put into the vault. Romeo goes there and commits suicide. The last lines of the play mention a morning, which would be Thursday. Shakespeare made a lot happen in a short amount of time.