found another thread on apneaboard that discussed resetting the clock.
that thread had a further link to:
In a nutshell, one user named Evergreen was resetting the clock to fix an error/oversight by the DME, and in the process of moving forward a couple of hours, clicked the date over to the next day.
Similar problem: system clock shows tomorrow for the date.
When he tried to roll the clock backward, got an error data already exists on that date. The machine apparently tries to preserve the integrity of compliance data by not allowing you to stomp on any date that has data collected. In his case that even meant a day he didn't use the machine, which had logged data indicated zero usage that day.
He ultimately blew away all the compliance data and reset from scratch.
Paula02 chimed in to say it is possible to change the date and provided a link (second link above) to a page on how to do it.
It seems like the catch here is you can't stomp on data that has already been logged. Furthermore, it seems like the machine has two kinds of data you can't step on:
1. date - summary compliance already logged for the date in question
2. hourly - session detail data already for the hour of the day in question.
All this suggests that it might be possible to slide the clock backwards within the same date, provided there was not a session after the target time you are trying to reset to.
A possible scenario: move the clock back over a two day period to get it back in synch with real time and not lose historical data (except for the two days you will munge making the adjustments).
step 1: late one night before midnight... roll the clock backward to some point in the hour following the time you ended the previous session. (e.g. this morning you got up at 8:15 and turned off the machine. Tonight at 11:30pm you reset the clock backwards to 9:30am.)
the clock was moved back 14 hours, and is now ten hours ahead of real time.
step 2: sometime before 2:00pm (CPAP clock is ten hours ahead so 2:00pm is when the CPAP clock reaches midnight), roll the clock back however many hours you can to the hour after the previous session ended. (e.g. this morning you got up at 7:15am (CPAP clock time 5:15pm) and turned off the machine. At 1:45pm when the CPAP clock reads 11:45pm you reset the clock backwards to 6:45pm. That gives you back 5 of the 10 hours you still need.)
the clock was moved back 5 hours and is now 5 hours ahead of real time.
step 3: sometime before 7:00pm (CPAP clock is five hours ahead so 7:00pm is when the CPAP clock reaches midnight), roll the clock back again to the correct time. That gives you back the final 5 hours, and now the date and time are correct on the CPAP clock.
1. you must reset the clock within the same date and therefore it is necessary to act before the CPAP clock reaches midnight and clicks into tomorrow.
2. you must reset the clock to a time in the hour following any hour that has session data already logged so that there is no data to stomp on in the target hour.
This is a heck of a convoluted way to recover the clock back to real time of day, but based on what I have read it might work.
The alternative seems to be to blow away the machine and lose all the historical data stored in it.
No idea how your CPAP clock got into tomorrow's date, but above is a potential solution to reel it back in.