My 3575 and 3576 were both unable to get the time from the PBS station because a community FM station that has its antenna less than a mile from my house was creating a lot of interference in the channel 6 spectrum. (I recently got it going again by switching in the FM filter in my CM7777 pre-amp and adding an FM trap in front of the pre-amp.)
I believe the time drift was less than a minute per month. If my units are typical, it shouldn't be the end of the world, unless your trying to do back to back recording.
Its my experience that one can still have a problem trying to record back to back, even if the recorder is dead on. I have noted that sometimes one station will start the later program before the earlier program is completely over on another station. In my area, it is more of an issue during first runs when they often have a preview of the next weeks show. I would sometimes have to give up some or all of the preview to get the lead in of the second program.
I usually set up to start 2 minutes before the scheduled beginning and go 2 minutes after the scheduled end to be sure I get everything.