There is no real time clock on the unit. I'm not sure why they left it out.
I think it is most likely that Rigol left out the RTC quite deliberately, despite the low cost of adding one. Like almost all companies, Rigol need to find good ways to segment their market -- take as much market share from the competition, but make sure that they do not cannibalize their higher-end scopes too much. Adding all the measurement and analysis features which make the DS1000Z series an "offer you can't refuse" in the amateur, entry-level and educational market, but leaving out a few features which professional users find important, is a perfect way to do that.
CAN decoding functionality is probably another example: Could have been added without extra hardware cost, and maybe even sold as a separate upgrade option -- but it is not available, since it is a typical requirement for the professional space. "If you need that, buy a 2000 series or higher model"; makes perfect commercial sense. I can't blame Rigol for that; they are in this business to make money...