- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

dispatch_time_t delay = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_SEC * 0.5);
dispatch_after(delay, dispatch_get_main_queue(), ^(void){
    // do work in the UI thread here
});

NSTimer *timer;
...
timer = [[NSTimer scheduledTimerWithTimeInterval:30.0 target:self selector:@selector(thisMethodGetsFiredOnceEveryThirtySeconds:) userInfo:nil repeats:YES] retain];
[timer fire];

- (void) thisMethodGetsFiredOnceEveryThirtySeconds:(id)sender {
   NSLog(@"fired!");
}

+[NSTimer scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:]