What you are doing is not unusual. Where my kids went to HS, anyone having a first period study hall didn’t have to show up until the start of second. Anyone with a last period study hall could leave early.
My kids never had a study hall until they were HS seniors. Oh…and in addition to only taking six classes, they each took Culinary Arts as one of their courses. They both got accepted to the colleges of their choice (which they well vetted before applying).