Act III, scene 5, opens with a disagreement between Romeo and Juliet. What is their disagreement and how is it settled?
They are trying to determine whether it is night or day. This is important because their plan was for Romeo to leave before the watch for the day was set. They tried to use the light they could see outside, as well as the birds they heard singing. They argued between the bird making noise as being the nightengale or the lark. One represented morning, the other night time.
They ultimately figure out it is day, but I think this is more because they are disturbed by the nurse who is there to warn them before Lady Capulet walks in on them. Likewise, they agree that they do not quite want Romeo killed just yet by the watch.
What they are disagreeing about is what kind of bird they hear calling. Juliet is trying to say that it is a nightingale and that it is still night so Romeo will not leave. Romeo is saying it's a lark and that means it is morning so he must leave or be killed.
After they argue it that way, they switch sides. He doesn't want to leave because he loves her more than life. She wants him to leave because she can't bear to have him killed.
Finally, he has to leave when the nurse starts calling for Juliet.