It is from the Sunnah that if someone marries a virgin, he should stay with her (the virgin) for seven days and then divide the nights between them. But if he marries a previously married woman, he should stay with her for three days, then divide the nights (between his wives)

It is a directive from the Sunnah that when someone marries a virgin, he should stay with her for seven days to keep her company, and to remove her loneliness and also her shyness about the fact that she is recently married. He should then divide his time equally between his wives. If he marries a woman who was previously married, he should stay with her for three days, as her need is less than that of the virgin’s.
This wise ruling is implied in this Hadīth reported directly from the Prophet (may Allah's peace and blessings be upon him) because when narrators say: "It is from the Sunnah," they can only mean the Prophet's Sunnah.