Why does Juliet have to fake her death a day earlier than planned?

Juliet’s dad said that she has to marry Paris but she refuses.

Her dad gets angry and said that if she doesn’t marry Paris, then he’s going to disown her forever.

So, Juliet goes to Friar Lawrence and they come up with a plan so that Juliet can be with Romeo (seeing as Romeo is exiled from Verona).

So, she drinks a potion the night before her marriage to Paris. In the morning, she does not wake and she is pronounced dead.

Her family take her to the Capulet tomb where she will wait for Romeo.

Friar Laurence writes a letter to Romeo informing him of their plan, however, the letter doesn't get delivered to Romeo and he is told that Juliet is dead.

Then Romeo drinks the poison just before Juliet wakes up.

And Juliet sees that Romeo is actually dead so she kills herself with a dagger.

Hope this helps :)