Most 'big businesses' I've delt with have a time server someplace internal. It may be a stand alone NTP server, a network device like a Cisco router or a Windows AD server. You might ask the network team/Windows admin team nice and see what they have.
replyA great solution I've used plenty of times is to query websites like google.com. I use it whenever my rtc on my Linux laptop gets reset (as long as it's still in my history. Otherwise I just set it manually).
replyGPS unit
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