when i worked in emergency services i worked 12 hour shifts for many years. they were a 2 on, 2 off, 3 on, then reverse for the next week. it sucked for scheduling anything weekly. i liked having a 3 day weekend they other week though. the other shitty part was covering absences which meant working 18 hours with only 6 off between shifts which meant about 3 hours sleep with a 45 minute commute. four 10s on a regular weekly schedule is way better.