To set the time on a linux box to one of those goverment time servers use
ntpdate time-b.nist.gov

Ex.
[digerati@rh9 /]$ ntpdate time-b.nist.gov

For those in different areas of the world you can use the 'pool' of time servers.

NTP Time Servers

It should be noted that the above time server is actually 'restricted'. See
TimeBNistGov

I would suggest using:

'uk.ntp.pool.org' (you can normally just replace the 'uk' with your country code)

Or just 'ntp.pool.org'