So, it turns out that the BeagleBone (or the BeagleBone Black for that matter) does not have a battery back-up for its clock, so it loses the time every time I turn it off. It is mentioned on some websites that you have to set up an NTP access to fire on bootup to keep the clock set to the current time, but of course my application is off the network. It turns out that a few people have made something called a Real Time Clock cape that has a button cell and a particular single-chip solution to act as the Beagle Board's hardware clock. Unfortunately, the nicest of these, originally sold by BeagleBoard Toys, is no longer being made.
Presently, a multipurpose board sold by Waveshare has an RTC chip and a battery. It can be bought from the company, or interestingly from Amazon.
It is also possible to either hook up the Adafruit RTC stamp to a cape protoboard as described in this article, or completely build the BeagleBoard Toys design on a protoboard.
This article shows what commands to use to set the time on the adafruit RTC stamp once the RTC cape using it is assembled.
This forum thread has more info about different RTC chips that can be used for this sort of project.
