In his discussion about the validity of Sacred Texts, in Nyāyamañjarī 4, Jayanta seems to propose a similar argument, since he says that:
Nor are they (dharmaśāstras, i.e., texts prescribing ethical and social norms) based on experience, since sense-perception is not able to determine a duty which has the form of something to be done and is not determined by the three times.
What does "not determined by the three times" (trikālānavacchinna) mean? The Granthibhaṅga (the only ancient commentary on the NM) describes the three times as the domain of sense-perception. I would add that dharma escapes the three times (past-present-future), insofar as it belongs to neither of them. It belongs to a modal, not temporal dimension. Therefore, it is not "eternal" in a temporal way.
I already discussed the impossibility of sense perception to grasp dharma in this post (from the point of view of Mīmāṃsā).