My elementary school (early-mid 1980s) started at 9 am and ended at 3 pm
Middle School was slightly earlier, but I can't remember the exact hours...I think something around 8:15-2:30 ish.
High School I had moved to a different state. My schedule started around 7:30 am and ended around 3:30 or 4 pm. But that's because I took an optional "elective" class. Many students who didn't take the optional elective ended about an hour earlier than me.