Davex/doc/help/SetDate

setdate -- a crude way to set the date

syntax:  setdate <month> <day> <year> <hours> <minutes> [-p]

ex:      setdate 4 10 88 22 40     --April 10, 1988 at 10:40 pm
         setdate 4 10 88 10 40 -p  --same date
         setdate 3 28 67 0 10      --March 28, 1967 at 12:10 am

'setdate' is a straightforward command for setting the
ProDOS date and time.  -p means "p.m." and is the same as
adding 12 to the hours value.

'setdate' is useful only if your Apple does not have a clock
card.  (The Apple IIgs has a clock built in; if ProDOS does not
know the time on your GS, it's because you are using ProDOS 1.1.1
or earlier.)

If you want to be weird, you can type BF06:60 from the monitor
to disconnect the clock driver from ProDOS.