Currently the wizard that configures SBCE only allows a single NTP source. While more can be configured in the operating system, those additional entries do not persist across reboots.
We recently had a connectivity problem to the primary NTP source, and found that all the SBC's internal clock drifted so far that they essentially lost synchronization with the EMS, so having the ability to configure multiple NTP sources would allow it to maintain a more stable environment, as well as be consistent with all of the other applications in the Aura suite.