“Jesus said that there are twelve hours in a day but it is not like that in this our time for we have twenty-four hours and I want to know why it is so.”
To the Jews, there were twelve hours of daylight and twelve hours of night, thus making twenty-four hours total. During the winter months, when the time of daylight was less than night, their daytime hours were shorter to compensate. “The Jews divided the day from sunrise to sunset into twelve equal parts.” (Barnes New Testament Notes on John 11:9)
I hope this answers your question.