Miles & More (Lufthansa, Austrian, Swiss, and other partners) - FCT or FCL access 18 hours before a flight

I'm flying LH in C from Malta to FRA – arriving at 15:35, then departing in F on LH to DFW at 10:20 the next morning.

Can I access any of the lounges in FRA before I walk over to the Sheraton for some sleep?

I'm flying LH in C from Malta to FRA – arriving at 15:35, then departing in F on LH to DFW at 10:20 the next morning.

Can I access any of the lounges in FRA before I walk over to the Sheraton for some sleep?

No. Your arrival shorthaul C BP won´t grant you access. And as you´ll only be flying F the next day you won´t have access to any of the F lounges.