There has been relatively little work on the implementability of timing requirements. We have previously provided definitions of fundamental timing operators that explicitly considered tolerances on property durations and intersample jitter. In this work we identify three environmental assumptions and compare the implementability of a Held For operator in each of them, formalizing this analysis in PVS. We show how to design a software component that implements the Held For operator and then verify it in PVS. This pre-verified component is then used to guide the design of more complex components and to decompose their design verification into simple inductive proofs as demonstrated through the implementation of a timing requirement for an example application.