A replset member can detect clock skew between itself and a newly elected primary by checking the timestamp in the newly-elected member's election id, and comparing that to the local time when the member has first noticed the other member becoming PRIMARY. This requires that there be a recent previous heartbeat (eg. < 10s ago) showing the other member in not-PRIMARY state.

This is motivated by replset clock skew > 30s having more effect now that election ids are being used to notice stale primaries.