When I first got my Nexus 4, the "time to leave" notifications from Google Now were reasonable. I'd get a notification at 9:30am saying that I should leave at 9:45am for a calendar appointment.
After a few weeks, however, the notifications stopped arriving at a sensible time. The best case scenario is that I'll need to leave at 1pm for an appointment and get a reminder at 1:15pm (after I'm already on the road) saying that I should leave at 1:15pm to arrive on time given current traffic. I may also get a notification at 1:15pm saying that I need to leave at 1pm. Since I don't own a time machine, this isn't very helpful. This happens for all of my calendar entries that have an address. The late notifications are rather consistently 10-15 minutes after the time that I think I should leave for a destination.
I found this question which might be related, but my notifications are showing up late rather than displaying absurd times.
Is this a known issue? Is there a workaround?
The alt-text for today's XKCD is
It ships with a version of Google Now that alerts you when it's too late to leave for your appointments.
That seems to confirm that this is a bug other people are experiencing, but I haven't had much luck finding bug reports about it since the search terms are too common.