I definitely think the time limit above MCT is important and that exceeding MCT after the the relevant time limit, even if only by a small margin is not allowed.
I doubt that the performance experts would leave one so badly placed on the OEI escape route that one would have to exceed MCT. However one can end up badly placed in the route for other reasons such as a load sheet error...therefore, if the need truly arises to use more thrust, up to full thrust I would definitely not worry about the time-limit...I don't think the engine will simply disintegrate because one has exceeded the time limit...
