My MythBox seems to have lost some time - it's been missing the first 30 seconds or so of every recording. Sure enough, the system clock was off. At some point, somehow, my time server updates stopped working. I'm not sure what I did to knock it out of whack, and don't care to sink too much time into this right now, but here's what I did to get it back in order.
Check your date with the "date" command.
Wed Apr 1 23:12:09 EDT 2009
Verify that date against time.gov.
If it seems off, you can sync up with a time server manually with the 'rdate' command:
root@mythtv:/root# rdate -s nist.expertsmi.com
That's just one of the time servers I found - I don't remember where. After that, do another check and you should see your time sync up with time.gov, and your recordings will start on time. When I get around to looking into what happened with my time server synchronization, I'll write a follow-up post.