Internal - external Timeserver settings

I have not seen a way to do that. But to combat this, I have edited the Authorizations database to allow non-admin users access to the Date & Time System Preferences Pane. Doing that allowed users to update their time server to anywhere else if needed. See this post by the great @rtrouton - https://derflounder.wordpress.com/2014/02/16/managing-the-authorization-database-in-os-x-mavericks/

Here ya go, we have two set, for internal and external. Internal is first, if it can't find that, it will failover to the external which we set as apples.

#!/bin/sh

# Use "/usr/sbin/systemsetup -listtimezones" to see a list of available list time zones.
TimeZone="America/Charleston"
TimeServer1="YourTimeServer"
TimeServer2="time.apple.com"

############# Pause for network services #############
/bin/sleep 10
#################################################

/usr/sbin/systemsetup -setusingnetworktime off 

#Set an initial time zone
/usr/sbin/systemsetup -settimezone $TimeZone

#Set specific time servers
/usr/sbin/systemsetup -setnetworktimeserver $TimeServer1
echo "server $TimeServer2" >> /etc/ntp.conf

# enable location services
/bin/launchctl unload /System/Library/LaunchDaemons/com.apple.locationd.plist
uuid=`/usr/sbin/system_profiler SPHardwareDataType | grep "Hardware UUID" | cut -c22-57`
/usr/bin/defaults write /var/db/locationd/Library/Preferences/ByHost/com.apple.locationd.$uuid LocationServicesEnabled -int 1
/usr/sbin/chown -R _locationd:_locationd /var/db/locationd
/bin/launchctl load /System/Library/LaunchDaemons/com.apple.locationd.plist

# set time zone automatically using current location 
/usr/bin/defaults write /Library/Preferences/com.apple.timezone.auto Active -bool true

/usr/sbin/systemsetup -setusingnetworktime on 

/usr/sbin/systemsetup -gettimezone
/usr/sbin/systemsetup -getnetworktimeserver

exit 0