Book online for 7 days, check in on the evening of 24th and check out at noon on 28th. In that case, when can I make a reservation online?

If you check in on the evening of the 24th, arrange to check in on the 24th and book on the 27th. Because all hotels check in on the same day, they can check out before 12 the next day, so as long as they check out before noon 12 on the 28th, if they temporarily change their plans when they check in and want to stay for a few more days, they can directly contact the front desk to make a reservation, that is, four days.