An alternative to using NTP, is to relaunch just the time setup portion of the amp-install. This can be done from the CLI as follows:
# cd /root/svn/mercury/install
# ./time-setup
[root@amp1 install]# ./time-setup
------------------------ Date and Time Configuration ---------------------
Current Time: Mon Nov 11 12:43:47 PST 2013
1) Change Date and Time
2) Change Time Zone
0) Finish
Be very careful when changing the time. DO NOT change the time to be in the future (in other words be very careful if changing the date) as it will affect all RRD files. The RRD files will then not collect any data that looks older than the last update. Recovery from such situation is either to restore a previous backup, or blow away all RRD data.