Give a time between tasks - iOS

I'm removing my plcae position from a iPhone's GPS. we wish to get a
coordinate from a same indicate 15 times (to get a best plane accuracy).Is
there a proceed to wait for example, 2 seconds between one coordinate and
another?I use an vigilant called coordinate, with embodiment and longitude
as property..... Exemple codeCoordinate * coord = [[Coordinate alloc]
init];NSMutableArray *coordinates = [[NSMutableArray alloc] init];for (i=0
; i<=14; i++){ coord = newlocation; [coordinates addObject:coord];
.... some formula to wait 2 seconds before supplement a new vigilant to a
array....}I attempted to use NSThread sleepfortimeinterval, though a
perspective freezes.Thanks