.h file

// declare timer 

NSTimer *countDownTimer;
@property (nonatomic, retain) NSTimer *countDownTimer;

.m file

// stop the timer before it is used
// this is useful sometimes if not the timer might be run twice
[self.countDownTimer invalidate];

// this will create and RUN/SCHEDULE the timer all at the same time.
self.countDownTimer = [NSTimer scheduledTimerWithTimeInterval:2 target:self     selector:@selector(callBackFunctionHere:) userInfo:nil repeats:NO];

ObjectiveC NSTimer

Objective C