How can I make an iOS device a NTP server ? The reason for this is, the network of devices I have don't have internet connection but are connected via Wifi. So just want to create a device as a server and let others to associate themselves to it.
I'll quote two answers from Stack Overflow with the hope that it will help you figure out what you're trying to do.
There's a small iOS library named ios-ntp. I have used it in one project in the past and it seemed to work reasonably well.
As of mid 2013 the original ios-ntp project has a few missing pieces, so I have mirrored the original svn repository to github. You can checkout out a working version of the code here: https://github.com/jessedc/iOS-ntp
If you're not developing a commercial application, peek at the linux source.
Just use dns to intercept requests to time.apple.com and point to a local Linux or raspi serving ntp. Of course, you will need to set up a dns for this to work.