Last I have heard, there is a known problem that the first RAW file created by CHDK (since the camera was turned on) will give the wrong date/time (for my A720IS, it is always something like 01-01-2001 12:00am--or something like that). After the first shot, the rest of the date and times were correct.
As I understand, the function that initializes the date/time parameter has not been found (at least in the DRY OS type cameras). Until that function is found--I believe that this will continue to be a problem.
-Bill