I was configuring a C800 for DDR when I came to the idea to implement timed access-lists too.
There is a problem due to the nature of the clock in low-end routers that causes the clock to be initialized to some date in the past when powered on. I remember I had seen a configuration sample, (I'm quite sure it was on the German CCO pages), where this problem was solved allowing a one-time dial-up call to reach the NTP server and after that correctly applying the time-based rules to any further call attempt.
I'm no longer able to retrieve this sample or any somilar other, nor more info on the topic.
Maybe somebody has saved the sample or has one on his own to make available ?