Is a man married to two women required to allocate specific days for each wife, or is he permitted to divide the days between them, especially if he visits one of them after his time with the other has ended, merely for intimacy, which causes the second wife to feel injustice?

A husband must be just between his wives, and this includes justice in division, meaning spending nights with each wife equally, whether one night or more. This is an obligation by the consensus of Muslims. The husband is not held accountable for the inclination of the heart if he is just in the division. Whoever does not deal justly between his wives will come on the Day of Resurrection with his side inclined. He must fear Allah and be just in the division, and the wife should remind him of that.