After configuring ntp in the SSIM 4.8.1 Web UI the time will sync once and then stop.
Symantec has determined that this is because of a incompatibility in an OpenSSL rpm and ntp rpm.
This will be fixed in SSIM 4.8.1 Patch 1. If you need this to be addressed before SSIM 4.8.1 Patch 1 releases you can download and apply the attached 4.8.1_Hotfix-1.