When you're time travellers, the concept of a day — from midnight to midnight — can get lost: the Doctor and his companions arrive on different planets in different eras at different times of the day. They can show up during someone's lunch break or when they're asleep, at the breaking of dawn or the coming of night. Time, it seems, is very much of the essence... day n. : 1: a period of twenty-four hours as a unit of time, esp. from midnight to midnight. 2: a point of time. "I can't make your dream come true forever, but I can make it come true today." - Doctor Who by Matthew Jacobs