If we begin by looking at Act 3, Scene 4, in line 18, Paris notes that the day at that time is Monday. We also know that by backing up a bit to Scenes 2 and 3 of that same act, both Romeo and Juliet reference being married on that same day, a few hours prior. They only met the day before. So the timeline looks like this:
Sunday: Romeo is pining over Rosaline when he attends the Capulet ball. He sees Juliet, and they fall immediately in love. The famous balcony scene entails.
Monday: Romeo and Juliet are married. That same evening, he kills her cousin and is banished.
Tuesday: Romeo leaves for his banishment after spending the night with Juliet. The friar hatches a plan with Juliet; she should take a drug to make her appear dead and escape to be with Romeo. Juliet drinks the drug on Tuesday evening.
Wednesday: The Capulets find Juliet's "dead" body.
Thursday: Romeo learns of Juliet's "death" and heads back to her tomb. He kills Paris, kills himself, Juliet awakes, and then she kills herself.
These star-crossed lovers only shared 5 days together—and even all 5 were not shared in physical presence. Likely this was Shakespeare's intent—to show his audience that time is fleeting and is quickly passing us all by.