Make sure you are in sneak mode before entering the house. If the eye is dim then you are not being watched as you enter. If the eye is bright you can enter but you are also being watched as you enter, so the guards are likely to grab you when you exit (or even before you exit).
As for people being awake or asleep, that's a matter of "casing" them and learning their habits, including when they like to sleep. Some people sleep the night away, some are night owls.