Run this in a command prompt:
w32tm /config /manualpeerlist:"time-b.timefreq.bldrdoc.gov,0x8" /syncfromflags:MANUAL
net stop w32time
net start w32time
w32tm /resync
net stop w32time
net start w32time
w32tm /resync
The flag "0x8" sets the SBS server in client mode.
More information can be found here – http://support.microsoft.com/kb/875424