i used the C section at CW to go from exempt to 90 day Non O - retirement. 2017 and 2021. both times there was not much of a wait. one or two people in front of me. if you can get an appt that's great, but probably not much of a wait if you go in person.
for me, the C desk has been the area that takes the least time if you go with no appt, compared to O extensions, 90 day reports in person, tourist visa extension, re-entry permit, etc.....