PaulS:
You misspelled considerable.Why do you need to tell the RPi what time it is? It has a clock.
The RPi has no RTC and is getting it's time with NTP from the internet (timeservers).
Without a RTC and internet you lose the time after reboot.
I get the time from DCF77: DCF77 - Wikipedia
Then the RPi is the timeserver where all other network devices get the time from.
https://www.meinbergglobal.com/english/products/ru226.htm
https://www.meinbergglobal.com/english/products/ntp-time-server.htm