One easy solution is to connect SM App to StellarMate, this would sync time + location. You don't need to use StellarMate App afterwards, but it syncs both time and location upon connecting to the unit automatically. Other options include RTC clock or better GPS dongle. The App seems the easiest route.
Thanks. It never occurred to me that StellarMate was writing the FITS file until I saw the screwy time in the header. When doing Variable Star work, the people who receive the reports like to have the time expressed in terms of solar system barycentric time for stars with really short periods, cataclysmic, etc. My control room clock is usually accurate to 60 ms according to a link to the NIST web site.
That is strange.
Can't the raspberry pi set the time with a command like the following?
sudo date -s '2021-01-04 13:04:00'
You might want to stop ntp once beforehand.