A day room is a room you can use for a few hours on that same day (short stay). Some hotels will provide you with a 4 hours time period, some will be more generous and give out 8 to 9 hours. However, please note that you must absolutely check out by the time listed on your booking confirmation, or you may be charged extra.
Additionally, please note that you cannot change the hours listed. Any attempt to change the hours must be required at the Hotel front desk, subject to the hotel’s approval, depending on their local booking conditions, and subject to a rate difference - if any.