I just posted over on Apple's boards but the theme seems to be constant. There is a problem with the Airport Extreme Base Station and version 5.4 of the Firmware. The problem manifests itself as the Base Station loosing its internet connection every 24 hours. The problem lies in having the base station setup to use the network time protocols for syncing its clock. The clock on the base station really doesn't matter unless you want the dates to show up correctly in logs (and you have remote logging turned on) so there are probably only a handful of people who will encounter this problem. The workaround is to have the base station not report in the correct time and to set the log file to "mark" the log instead.
below is an excerpt of the log file. The times by the way are UTC, not the local time zone, so people will see the problem occurring at different times ranging from about 8am to Noon in the continental US.