there's a network time control panel you can get on macintosh repository that should use ntp to whatever server you want (I use time.nist.gov) to set the time on boot if it's inaccurate
I should've mentioned, I want to do this
without networking as well. I'm well aware of the various options that exist for that.
Or, it must check against some standard date stored (I’d assume) in the System.
The time/date is stored in a global variable and the clock chip. That's why a PRAM battery is needed to
keep the time between power cycles.
Make an extension that sets the time to some time in the 90s before the finder launches?
I thought this would exist already, but perhaps not. A few searches on Mac Garden didn't turn anything up yet. Most time/date utilties are for setting it from a remote time server.
The function
setDateTime
for setting the date/time in the system global variable
Time
and the clock chip are described in
Inside Macintosh: Operating System Utilities.
I do wonder if there's something I'm not thinking of that will mean this won't work though. I have no idea how this stuff is handled by Mac OS, in terms of, how it handles no date/time, what actually makes it think there's no date/time, and which bits of software are reading/setting it, and at what points they are doing that throughout the boot/startup process.
I'll give a few things a go and see how far I get, assuming this is a good starting point.