USB C standard insertion depth?
From what I can gather, it seems like the outer surface of the case needs to be 6.2mm from the deepest part of the socket. From the USB Type C connector and cable assembly compliance document page 51:

The continuity test fixture shall provide a planar surface on the mating side located 6.20 ± 0.20 mm from the receptacle Datum A, perpendicular to the direction of insertion.

However this document seems to be concerned mainly with test setups for USB-C so I am yet to get an authorative answer on this.