Definition of "bedtime"

I read every evening, sometimes late into the night, with the help of kerosene lamps, often secretly, past my bedtime.

2004, Vartan Gregorian, The Road to Home: My Life and Times, page 55

Irregular bedtimes may disrupt healthy brain development in young children, according to a study of intelligence and sleeping habits.Going to bed at a different time each night affected girls more than boys, but both fared worse on mental tasks than children who had a set bedtime, researchers found.

2013 July 19, Ian Sample, “Irregular bedtimes may affect children's brains”, in The Guardian Weekly, volume 189, number 6, page 34