Unlike full license FM stations, LPFM stations are not required to broadcast full time
§73.850 Operating schedule.
(b) All LPFM stations are required to operate at least 36 hours per week, consisting of at least 5 hours of operation per day on at least 6 days of the week; however, stations licensed to educational institutions are not required to operate on Saturday or Sunday or to observe the minimum operating requirements during those days designated on the official school calendar as vacation or recess periods.
When I was a kid, I listened to WPRB, Princeton, NJ, full commercial Class B on 103.3. I still remember the promo they ran in May/June one year that went something like this “Here’s a sample of our upcoming summer programming on WPRB …. sssssssssssssssssss (static)” A very unique station to this day, to say the least.