We have 2 GSTLs and 5 GSAs.
A couple of GSAs (including myself) are part-time and only work certain days or weekends. But if I ask for 40 hours during a week that I'm off at my other job, I can usually get them.
One of the GSTLs is a senior, so she does 1-2 LOD shifts per week. She also does our scheduling, so she writes a GSTL schedule for the month that looks similar to the ETL schedule, and tries to rotate us fairly with early, mid, and late shifts, including service desk and cashier. So, on a typical week with 40 hours, I would have 1-2 opening GSTL shifts, 1 closing GSTL shift, 1-2 opening service desk shifts, and possibly a mid cashier shift.