Elena's bed is next to Aeron's, and at certain times she will be sleeping or sitting on her bed. She will also go to sleep every time she eats some flesh. The bed cover can be changed to a different colour by giving Elena a drape, such as a red drape and a cat's-eye drape, and asking her to make a bed cover rather than a tablecloth.
The time will also affect certain aspects of the Towers. Time will pass in the Towers, so even if you enter at day you may come out at night. At night, the Towers are more dangerous. There are more enemies, and often they will be different or stronger than the ones you fight at day. At the same time, some enemies will be sleeping at night when you enter the room, as indicated by some bubbles above their heads. This gives you a chance to get in the first attack or to sneak past, although they will wake up if you move too close to them. The time will also affect which fountains you can drink from, restoring your health.