nfc – How is the timer implemented in mutual distance-bounding protocols?

I’ve come across several papers introducing the concept of mutual distance-bounding, where basically both sides can verify an upper bound of the distance in between, rather than having this unilateral relationship between a verifier and a prover. Although promising, these papers do not address the fact that in relay attacks the prover is usually an NFC capable card or chip. My question is, how can we implement a timer on this card to actually perform mutual distance-bounding protocols?

For reference, see Mutual Distance Bounding Protocols and SECTOR: Secure Tracking of Node Encounters in Multi-hop Wireless Networks.

This is a follow up question for this but in a broader context.