Is that a new feature? I don't have it on my switch:
HP-Lab-SW1(config)# ntp
authentication Configure NTP authentication.
broadcast Operate in broadcast mode.
enable Enable/disable NTP.
max-association Maximum number of Network Time Protocol (NTP)
associations.
server Configure a NTP server to poll for time synchronization.
trap Enable/disable NTP traps.
unicast Operate in unicast mode.
Is this a version difference? I'm running 16.03:
HP-Lab-SW1(config)# show flash
Image Size (bytes) Date Version
----------------- ------------ -------- --------------
Primary Image : 21989831 07/06/17 WC.16.03.0005
Secondary Image : 21989831 07/06/17 WC.16.03.0005
Boot ROM Version
----------------
Primary Boot ROM Version : WC.16.01.0003
Secondary Boot ROM Version : WC.16.01.0003
Default Boot Image : Primary
Default Boot ROM : Primary