There isn't any perk to be unlocked but you get the "no time for love ending", I guess. If you are going with Toru, as long as you are lovers by Seiyuu Award, you don't have to unlock all his lover scenes to get his best end so I think you still have time. September to December is a long time. Completing his best end gives you max personality stats (knowledge charm affection) so it's pretty handy for next playthrough.
Thing is, I have Toru on almost 5 stars, and full red heart affection, and dated him dozens of Sundays. but he doesn't seem to confess, nor Haato. Been like this for a whole week spending time with him, so I wondered if it was stuck forever if I had missed any events. Guess I'll keep trying and see if it progresses... Thanks!