The gap between exams and graduation?

Sorry if this has been asked before. I sort of poked around the forums and couldn't find an exact answer to this question. To my understanding, (please correct me if I'm wrong) college entrance exams take place autumn into winter and final exams for 3rd year of high school happens at the end of January/beginning of February. What do 3rd year students do between this exam and their graduation in mid March? Are they required to attend classes or not? Do some of them just sort of show up to see the friends and club members they may be separated from soon? Thanks in advance.

for example, the entrance examination of university of Tokyo will be held from Feb. 25 this year. and the result will be on March 10. so, students (and parents) of other than Tokyo area who get in the university is super busy, because they have to find a place to live and move to there between March and the beginning of April. (probably they need to go back and forth to Tokyo several times.)
unfortunate students who fail to pass the examination will have tough time to decide their future, whether they take the next year examination or they get in other universities, like Keio and Waseda.

generally speaking, lower level universities want to get students earlier, i.e. in Autumn and early winter. so, you are right. they are not so busy and they have plenty time to enjoy the last high school time.

Thanks for the response.