Network function virtualization (NFV) and cloud based radio access network (C-RAN) architecture concepts constitute an essential foundation of the 5G mobile radio network design. Especially the envisioned splitting of RAN functionality into distributed units (DUs) at base station sites and centralized units (CUs) running in a centralized cloud offer significant advantages regarding energy efficiency, computational elasticity and cost reduction for mobile network operators (MNOs). This paper presents an exemplary implementation and initial evaluation results of a corresponding interface between DU and CU for an emulation of 5G New Radio (NR) based bandwidth part adaptation and related physical layer processing time monitoring in LTE eNBs. Such an interface will facilitate computational elasticity by means of processing time aware transmission parameter adaptation. The implementation is an extension of the FlexRAN framework for OpenAirInterface.