...and of course, this applies to any backend domestic DH --- not just Sat mornings.
However, on Saturdays many smaller fields have a limited number of flights which return to MEM in the early afternoon, and thus rebuilding the pairing for a legal rest period, IAW the CBA, can yield a rather significant extension.
In Sept there also seems to be an increase in the number of odd-ball, 3-day trips that may have a similar backend DH min layover construction.
Regardless, of what Sort City your trip transits (MEM, AFW, EWR, OAK) it's always wise to understand how the "timeliness of the sort" affects your trip pairing.