Typically the pool heat controls are locked up, and not adjustable by the guests. There are no temperature settings on the dials of the units, so they just have a color coded "range" stamped on the dial, from cool to warm. I would guess that our pool gets to roughly 80 degrees, and stays there both day and night.
The single most important thing you, the guest can do is to cover the pool with the pool blanket at night to prevent heat loss. If you don't, the pool will be cold in the mornings especially. The heaters are an air convection type of system, so they can only work when the air temp outside is above 55 degrees, which means they may not work at night, so important to keep the heat contained.
We swim in our pool at night all of the time, even in the cold periods or winter months, so shouldn't be an issue. I would suggest you check with the owner to make sure they do have a pool blanket for their home / pool.