No matter what frameworks we use -- Core Graphics, Cocos2D, OpenGL ES -- to write games, should a timer be used (for games that has animation even when a user doesn't do any input, such as after firing a missile and waiting to see if the UFO is hit)?

I read that NSTimer might not get fired until after scheduled time (interval), and CADisplayLink can delay and get fired at a later time as well, only that it tells you how late it is so you can move the object more, so it can make the object look like it skipped frame. Must we use a Timer? And if so, what is the best one to use?