Hi,
The behaviour of an IAP in terms of NTP is as follows,
1. By default, the IAP tries to connect to pool.ntp.org to synchronize time.
2. A different NTP server can be configured manually or from Central.
3. It can also be provisioned through the DHCP option 42.
4. The NTP server provisioned through the DHCP option 42 is used if no server is configured.
5. The default server pool.ntp.org is used if no NTP server is configured or provisioned through DHCP option 42.
To configure NTP server manually, use the following steps,
1. System>General.
2. Enter the IP address or the URL (domain name) of the NTP server in the NTP Server text box.
3. Click OK.and reboot
As a good practice always connect the IAP to internet and let it contact the Aruba central and sync with NTP and download the golden config.
Hope got some more clarity on this.