Conflicted on how to record my working times

I WFH 4 times a week. When I work from home I would be available on Microsoft team from 9-5, so would write that I worked 7 hours a day (minus 1 hour for lunch) on my time sheet. However I don’t get that much assignments to fully work 7 hours a day (just a summer job from my school so I think it’s very relaxed). But also on my acceptance letter, they said I would be working 35 hours. I am really conflicted on how I should record my time; by the times I am actually doing work assigned to me or by the time I am available?