Sentence:  Irregular bedtimes may disrupt healthy brain development in young children, according to a study of intelligence and sleeping habits.  &para; Going to bed at a different <WSD>time</WSD> each night affected girls more than boys, but both fared worse on mental tasks than children who had a set bedtime, researchers found. 
Meaning of the word marked with <WSD> tags:  How much of a day has passed; the moment, as indicated by a clock or similar device.