What is planned in Act 3, Scene 4 of Romeo and Juliet? How will this decision influence or change Friar Laurence's earlier plan?

In Act 3, Scene 4, Lord Capulet is in conversation with the county Paris, who has come to pay the household a visit. Lord Capulet informs him of their sorrow and Juliet's depressed state following Tybalt's sudden death. He tells him that he would have already been in bed were it not for Paris' visit.

Paris wisely states that such grave circumstances are inappropriate for him to seek courtship. He asks Lady Capulet to pass his regards to Juliet. She promises to do so and states that she will consult with Juliet the next morning regarding her sentiments about marrying the county, since Juliet is at this time too overwhelmed with grief to speak.

Lord Capulet then declares that he will speak to Juliet and says that he is confident that she will cooperate fully; in fact, he has no doubt about that. He then instructs his wife to speak to Juliet about Paris' love for her. Lord Capulet then tells Paris that he will arrange their wedding for the coming Wednesday. However, he soon changes his mind when he discovers that it is Monday and believes that there will not be enough time to make the necessary arrangements.

Monday! ha, ha! Well, Wednesday is too soon,
O' Thursday let it be: o' Thursday, tell her,
She shall be married to this noble earl.

Once Lord Capulet has told Paris that he will set the wedding for that Thursday, he wishes to know if the date suits the young earl, who replies that he would be overjoyed if Thursday was tomorrow. The wedding date is then finally set for Thursday.

This new arrangement will upset Friar Laurence's plan in which he advised Romeo, in Act 3, scene 3, that he should, that night, have a secret liaison with Juliet in her chamber when everyone is asleep. Romeo would thereafter flee to Mantua, where he would live until such time as they have brought together friends from both parties and sought a pardon from Prince Escalus. Once a pardon has been obtained, Romeo would return to Verona. The two young lovers would then publicly proclaim their love at an appropriate time.

Since Lord Capulet is planning Juliet's wedding for that Thursday, there won't be enough time to make the arrangements the Friar had in mind, for he has to somehow circumvent the wedding. The Friar does, indeed, later formulate a new plan with disastrous results.