I would put a cutoff point at about 11 or 12 or so for when you are on vacation etc. At least in my house there is usually not that much activity after midnight.
I do something similar and once recevied a complaint from a family member when we didnt answer the door yet they saw a light turn on inside the house (from the other side of the family and I guess they took it personally :angry: ) There was one car home and they swore someone was home so it does ehlp the house look lived in.
My only thought is that there is not enough randomness. I was thinking to maybe turn lights on for X minutes depending on certain events, such as phone ringing, temperature hitting a certain value, etc. Something someone watching would not know and would happen at completely random times.