If you used a standard lease the period is likely only 24hrs. It is not your problem that they have family staying with them.
I would tell them 24 hours. Their family problems should not become yours.
My tenants are moving out, they just closed on a house. They want 48hr notice in order for me to show it. I think that is a long time. Should I tell them 24hrs? They have family staying from out of town.