Although I have never had a need to impliment NTP server connection in any app that wrote but I came across of a sample project quiet sometime ago that helped me do it for the purpose of learning how to do it. The project maybe. A bit older but I'm possitive you get the idea from it and can write the work around for yourself. Anyway here is the link to to project: https://github.com/jbenet/ios-ntp
Although it is licensed as MIT and you may need to get a license from the developer or better yet just write your own. Hope this helps you out man.