Timeservers setting problem


I have problem specifying timeserver in profile. There are 3 predefined timeservers, but only http://timestamp.digicert.com works for me. Other two gets error 12999 during signing document.

When I try to define some public timeservers like 1.pool.ntp.org, or tik.cesnet.cz, I get error 12999.
If I add http:// to this timeservers (which doesn't make sense in case of NTP), I get error 12205.
I have direct connection to internet, without proxy.

Do I need some special timeserver, other then standard NTP? Or what am I doing wrong?

Thank you.

Jiri P.