I think there are some inherent flaws with your question, as how would your app determine what the real date/time should be? The user would need to be connected to data in order to fully verify, so if this is for a subscription or trial period, they'd find a way around it. If you're just looking for date, then I don't think it's terribly difficult, but time will be determined by time zone, if the user allows the device to select the "correct" one, daylight savings, etc.
Best suggestion I have at the moment is to write a query in your app that pings one of the global clocks to verify date, adjust the result based on the time zone of the device, then compare to what the device's date/time is set to.
Get the device's date/time (NSDate uses the device's clock):
-(void)targetMethod:(id)sender
{
NSString *currentTime = [dateFormatter stringFromDate: [NSDate date]];
timeLabel.text = currentTime;
}
Here's an example of an API for determining the correct time to compare NSDate to: http://worldtime.io/api/geo