Greg's age and mood is highly deterministic, and he has atoms in his body present from the big bang. His sense of time varies, and seems to accelerate as he gets older, and he will tell you about it with extreme detail down to either 2 decimal places or 3 beers. If you call him up and ask him what time it is, the degree of the obscenities used in his reply is usually a good enough correction coefficient when calling over long distances.
Also two of his kids hate him, and his current wife is thinking of leaving him; all countable metrics that one can use to ascertain what stage in his life Greg is at, and thus what the local date/time in your area is, based on all the above Greg stats.
Nah, all this is solved with star-dates. One of the Federation's crowning achievements - Warp Drive is small potatoes compared to getting hundreds of delegates from as many different worlds to all agree on one calendar system that is not based on their own world's orbit around its primary.. Diplomatic impossibility, but they managed it.
There is always the assumption that we will colonize the galaxy in 7000 years. When really we will still be on earth and someone is still running and old FreeBSD machine in prod and just doesn't want to update cause it still works.
While I doubt will be stuck on Earth in 7000 years, there's absolutely going to be some of those old systems with 7000+ years of uptime. Just throw the nanite repair gel on it every 50 or so years.