ntp

Generally, it's far preferred to run ntpd than to periodically run ntpdate.

ntpd will run constantly. It corrects time by adjusting the speed at which the kernel counts time, rather than changing the date directly. This approach means that you don't have any sudden jumps which can cause issues with software. It also means that any clock drift (as in, your computer's clock running ever so slightly too fast or slow, which is not uncommon on a VPS) is corrected for, preventing it from affecting the time. It is still common, however, to run ntpdate on boot, to ensure that ntpd has a relatively accurate starting time to work with; ntpd can't make big corrections to the time. It relies on keeping the time accurate rather than making big changes.

And the "in use" error sounds like you have ntpd running, but you're trying to execute ntpdate from cron everyday despite that.