Is it permissible to consider the reservation day as the start of the tenant's occupancy of the room, obligating him to pay rent for a month in which he did not utilize it?

The duration of the lease must be known, but it is not a condition that it immediately follows the contract according to the Hanafis and Hanbalis, unlike the Shafi'is. The rent becomes due for the agreed-upon period, and it is not a condition for its obligation that the lessee actually utilizes the leased property; rather, mere access to utilization is sufficient. It is recommended to be gentle and lenient in dealings, in accordance with the Prophet's (peace be upon him) saying: "May Allah have mercy upon a man who is lenient when he sells, when he buys, and when he demands his due."