I would love to know which scenerio you are expecting where you would have time to look + aim your sights in a self defense situation.
If you know how to acquire a target with your handgun, it would be most scenarios. It doesn't take time if you know how to point the gun -- the sights will already be there in front of your eyes. (For me, a Glock won't point worth crap, so I don't have or want any. That's the first thing I check: when I raise the gun, are the sights already aligned?)
Of course, you could be hip shooting, but short of that, the sights are useful if your gun fits you and you can shoot. You may not line them up very carefully, but they do tell you where the gun is aimed.
Too many people think that lining up the sights is a separate action from pointing the gun at the target. It's not, at least if you expect to be able to hit anything under pressure.