Just in these two lines, we have an example of the present perfect tense, "it's been a long day", and, at the same time, people use this statement as a phrase to express fatigue because they were extra busy that day or to express frustration.
在這兩句歌詞當中,「 it's been a long day」是現在完成式的例句,同時也可以用來表達忙碌一天後的疲倦感,或表達挫折感。