I added a pair of ocellaris clownfish to my tank 5 days ago and it seems that whenever i look at the tank they are swimming around no matter what time of day. All the other fish in my tank disappear when the lights go off.
Well, they become inactive or just less active overall. They'll usually hang out in a spot at night and stay there for the most part. If have an anemone, you may even observe them laying on their side occasionally.