All depends on who your hitting I guess. Someone who is not in GDI and double taps is probably not likely to care about the chances of getting hit by missiles or other harmful attacks against. These people probably wouldn't think twice about retaling a late retal.

But if you are in GDI, and you don't want to chance being hit with missiles or other harmful attacks that could mess up your set even more, you may reconsider retaling a "retal" no matter how late. According to GDI, any country who has hit you more than twice is fair game for anything, regardless of how spaced out those hits are, or if they are in response to hostile actions.