gistfile1.m

int64_t delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
	<#code to be executed on the main queue after delay#>
});


// Do something in the background and then when done call something on the main thread

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{

      // My Background blocking code, vars defined above this dispatch or class vars can be accessed here
      ...


      // Back to the main thread!
      dispatch_async(dispatch_get_main_queue(), ^{
										
		// update UI and what not, vars defined in the dispatch above or class vars can be accessed here, awesome scoping		
      });
});