The BeagleBone black do not have Real Time Clock and as a consequence each time you reboot, you’re back at time 0. To get it updated to the local hour, you can configure NTP client (if connected to network) using the following commands:

root@beaglebone:~# opkg update
root@beaglebone:~# opkg install ntp ntpdate
root@beaglebone:~# mv /etc/localtime /etc/localtime.old
root@beaglebone:~# ln -s /usr/share/zoneinfo/Europe/Paris /etc/localtime
root@beaglebone:~# killall -KILL ntpd
root@beaglebone:~# ntpdate pool.ntp.org
root@beaglebone:~# /etc/init.d/ntpd start
root@beaglebone:~# date
Sun Jun  2 17:41:10 CEST 2013