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… ...

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.