Does system clock affect asterisk cdr duration?

The cdr duration may have 1 to 2 seconds delay between asterisk and carrier.
As the total duration of difference is getting larger when the number of calls is static, I start to thinking what cause this problem.
I found that system clock is out of sync. And the ntpd service is turned off.
I know the T1/E1 card will synchronized with the carrier. But this is the only factor(system clock) I found.

So I wonder whether the system clock affect the cdr duration?
Will the CDR be affected if I adjust the system clock?