A network node includes a port and circuitry. The port is configured for communicating over a packet network. The circuitry is configured to receive, via the port, a sequence of packets from a peer network node, the sequence of packets including (i) a time-protocol packet and (ii) a transmit-side (TX) time-stamp indicative of a time at which the time-protocol packet was transmitted from the peer network node, to assess a receive-side (RX) traffic pattern over one or more of the received packets in the sequence that precede reception of the time-protocol packet, and to calculate an accuracy measure for the TX time-stamp, based on the assessed RX traffic pattern.