when i update a crontab job and then update the clock with "date" the crontab job doesn't start. I need to update the crontab after updating the system clock inorder it to be activated.
Does anyone knows why? and how to solve it?
btw it works aswell if i change the time and then restart the cron service

My guess, after thinking about how I would implement cron, is:

when you save the crontab file, cron finds the next time that one of the scheduled items should occur and the sets an alarm to go off at that time, then cron goes to 'sleep' waiting for the alarm.

This way cron doesn't have to waste a lot of cpu cycles checking each second seeing if something needs to run.

This implementation would explain both of your problems.

If you update the clock after updating crontab, cron has already set a timer, so it doesn't recognize the changed time. If you update the timer, then crontab, cron will set the timer based upon the new time. If you restart the cron server, it resets a time for the next entry.

Just an educated guess.