A day room, and why the house treats it as any other address
A day room is a hotel room taken for part of a day rather than a night, and once it has a number it is an ordinary address for a booking.
Hotels in the city let rooms by the afternoon as well as by the night, and a couple between a disembarkation and a flight, or between two sailings, sometimes takes one. The house has no special category for it. A room is a room.
What the thread needs
The same three things as any other booking: the address written out, the floor, and the room number. Add the hour the room has to be given back, because that, rather than the hour you would like to start, is what decides which lengths are sensible. A room held until four does not hold a session that ends at ten past four.
Check-in first, then the hour
This is the one ordering mistake that spoils a day room booking. The room number does not exist until the two of you have checked in, and a booking cannot be confirmed to a room number nobody has yet. Write when the plan is clear, agree the shape, then confirm the number as soon as you have it and let the forty to sixty minutes run from there.
Daylight, which is not a problem
An afternoon room has light in it, and people occasionally treat that as an obstacle. Curtains exist. Nothing about the arrangement assumes darkness, and an afternoon hour runs exactly as an evening one does.
The deposit on a same-day room
If the booking was arranged from home weeks earlier, half is ahead of it in the usual way. If a returning client asks for an hour or two that same afternoon at a city address, nothing goes ahead and the whole figure is settled on arrival, which the booking terms set out with the rest of the scale.