If you are sure that the Admiral or the President are Cylon it is ABSOLUTE top priority to brig them. Particularly the Admiral, who can burn your fuel into the ground (case in point). The flip side to that is that it is critical that you are not wrong, because brigging a human is just as bad. Roslyn needed to go on the hunt as soon as the sleeper phase happened (in fact, my first turn after the sleeper I would have Exec Ordered her to had I been human).

It's definitely designed to make it hard for the humans to win, but in that particular case once you all had seen me goof it up you should have brigged me so fast it'd make my head spin. It's a first-time mistake, really, and I've seen it happen twice (when I was playing with my Andy he made a small mistake that was also downplayed and nobody was sure enough he was a cylon to brig him so that later in the game he was the only one in the right position to take an Exec Order to let the humans win. I was also a cylon in that game).

So my considered opinion is that you have to be both decisive and right in acting against the cylons for the best chance to win.