Not any scarier than middle school.
Seniors are too lost in their own little worlds to really take much notice of the freshmen.
Plus it's really hard to tell that's someone's a freshman and not a sophomore or upperclassmen. And you couldn't fit a person into one of those lockers anyway. They take the whole class list and divide it so that there are equal numbers of people in each homeroom. About ten minutes is usually plenty the first day. The school is open around 7 AM, but most people don't arrive until at least 20 minutes before school starts.