hours output marker pulses

[Nick]

GPS is a bad idea for anything not needing navigation. It needs reception and is vulnerable. It's stupidly used  for loads of commercial applications simply to save less €200 on a €10K+ system so next decent Solar Flare like in 19th C there will be no Mobile, DTT or DAB most places.

NTP is a bad idea except to update occasionally as it needs the Internet, and thus has at least two vulnerabilities.

Both sweeping statements that I really have to pick up on. It may well be that this sort of accuracy is not needed, but to sweepingly dismiss both technologies in such a cavalier manner is, IMHO, unreasonable and incorrect.

Any sensible system will use GPS and/or NTP to discipline a local RTC of some sort to cover periods of outage. No sane person would design a system otherwise.

I have several systems that use GPS modules generating NMEA0183 $GPRMC sentences from which time and/or position data is extracted - such modules are cheap, reliable and readily available, e.g. https://uk.banggood.com/Beitian-BN-880Q-...rehouse=CN&rmmds=search and many others.

For internal systems I tend to use ESP8266 ESP-01 or ESP32 modules which are dirt cheap and have built-in WiFi and libraries for NTP etc.

You can even get NTP modules that emulate a GPS puck in that they generate NMEA0183 sentences and serial data - these are used inside buildings where no satellite visibility is available for systems that rely on GPS pucks - e.g. https://www.tindie.com/products/mazevedo...locks-kit/ - these are based on the ESP-01 module mentioned above and are extremely reliable - I use them on several of my classic nixie clocks - they'll even do DST handling for you, which could be important if you're using local time instead of UTC for your time stamping.