'Day' in the Bible

Say, O love of my soul, where you give food to your flock, and where you make them take their rest in the heat of the day; why have I to be as one wandering by the flocks of your friends?

Go out, O daughters of Jerusalem, and see King Solomon, with the crown which his mother put on his head on the day when he was married, and on the day of the joy of his heart.

We have a young sister, and she has no breasts; what are we to do for our sister in the day when she is given to a man?