you have to keep lights on 24/7 if your trying to see sex, if not the other 12 hours will be spent only hearing moans and other various noises.
yeah you dont have to tell me that was stupid i already know. but umm put them in darkness for 24 hours and it might show the sex sooner (but i dont know if this is 100% true so do research first) if not just wait it out, they will show just be patient.