The clock doesn’t have a 50 year run time because the batteries it’s designed to run on will self discharge in about half that. I’ve no idea what kind of battery could really last 50 years.

If you’re looking for a 1-second time reference, you’d probably just grab a GPS module off the shelf and use the 1PPS output. As demonstrated by [InazumaDenki], though, an old quartz cl… ...