I read (and use) a technique where I plug a
digital clock into an appliance module and
set up a timer to turn it off at 11:59pm
and on at 12:00am. Since most digital
clocks will reset to 12:00am after a power
outage, you can determine if the clock in
the CM15a is accurate by checking if the
time on the digital clock is accurate. I
wish I remembered who came up with this
technique so that I could give credit where
it is due.