In fact, it will be alright to say the prayer anytime you realize that you have missed it. In fact, it is essential. But the quality of that prayer would not be exactly the same as the prayer said in time. That difference would be there, you have lost that opportunity. Like you, if you are hungry, and at the crux of hunger, you eat. That is something very different from a time when after all your hunger is wetted by itself, not having anything. So when you eat, that is a different sort of food you eat.
So similarly is the phenomena of prayer, the prayer said in time, in a fresh mood, when you also realize that you are saying it in time, that is a different thing. And just to fill the blank by saying the prayer afterwards is a different phenomena.
