Is it permissible for a husband to spend the night of one of his wives with another wife if the first wife is busy outside the home or at a family gathering that the husband cannot attend, whether the time is during the day or at night?

Justice between wives is obligatory. There is no objection to the husband entering upon one of his wives during the turn of the other, if the wife whose turn it is is outside the home for work, a meeting, or similar reasons. This is because he is unable to fulfill her right due to an impediment on her part, and thus her right is forfeited at that time, whether it is day or night.