In Shakespeare's source for the play, Arthur Brooke's "The Tragicall Historye of Romeus and Juliet" (1562), the events take at least nine months to unfold (the time scale is very vague). As usual, in Shakespeare's tragedies, he compresses the time scale to a matter of days. The play takes four days in total, from Sunday through to Thursday morning.
Sunday - first scene and brawl in the morning, party that night, R + J meet, and balcony scene.
Monday - Romeo gets Friar Laurence to agree to marrying them. They get married the same day. Mercutio dies, and Romeo kills Tybalt. That evening, Capulet plans Juliet's marriage - and we know that that evening is on Monday, because Paris tells Capulet:
Monday! ha, ha! Well, Wednesday is too soon.
Thursday let it be— a Thursday, tell her
She shall be married to this noble earl.
Monday night R+J sleep together. Capulet and Juliet fall out about the wedding.
Tuesday. Juliet goes to Friar Laurence and gets the potion. When she apologises to Capulet, he brings the marriage forward a day:
Send for the County. Go tell him of this.
I'll have this knot knit up to-morrow morning.
Tuesday night, Juliet takes the potion.
Wednesday. Juliet is discovered "dead" and put into the vault instead of the marriage ceremony. Late that night, Romeo comes to the vault to commit suicide.
Thursday - "a glooming peace this morning with it brings" - the final lines of the play.