The next day happened to be a Saturday.
Claire had already set her heart on going to New York to see the concert and so, she proposed to Charlie that she wanted to take advantage of this opportunity to get to New York earlier as she wanted to take a stroll around New York, go to the concert at night, and then stay in New York for the night before strolling around New York for another day again tomorrow before they came back on Sunday night.
Charlie also felt that his wife had been working too