Sorry, dunno about without internet. There is openrdate which you might use in a cron job but I use sync-time-now-widget which adds a "Sync clock now" button to the system menu. I also make sure I only ever take the battery when I am within a WiFi zone. Although it could do it through a 2G or 3G internet connection if you don't mind risking a huge bill incurred by HAM trying to download a huge update at the same time.