Most owners lock up the pool heat controls, as you can do a lot of damage to a pool system by not knowing what to do with the controls (I won't even touch my own pool controls). That being said, the MCs usually set the pool heat to a comfortable 80 degrees (estimated)...so regardless of the outside temp, the pool will regulate itself to a comfortable temperature, just like the thermostat in your house works. Some will let you dial it up or down a little. On ours, if you touch the temperature setting at all, it shuts off for 5 minutes automatically. Rather than get lots of questions and complaints, it's easier just to lock it up, our MC will always come out and turn it up or down a little if someone asks them to.
Now, there's a few additional things to be aware of. First, without a pool blanket, and this involves you actually using it....the pool will most likely be cold in the mornings. Most of the heat will escape at night if you don't cover it up when it's not in use. Secondly, most of the pool heaters (not all, but most) are heat exchangers. They work kind of the opposite way your air conditioner works, they pull heat out of the air and put it into the pool (as opposed to like an electric or gas heater that actually heats the water). If the ambient air temp falls below 55 degrees, they won't work at all basically. Of course, in regards to my first point, this means the heaters won't heat at night much at all, so it becomes crucial to use a pool blanket.
Make sure the home you rent has a pool blanket! You can also ask what type of pool heater they have, if it's the heat exchanger type.
To answer your original question though, the pool heat should keep your pool plenty warm. The only time it's ever really an issue is if the temp stays below 55 for an extended period of time, then the MC tells me they get lots of calls from guests complaining the pools are too cold. Of course, there's not much they can do about it, this is how the heaters work! What they do find though, in most of the cases people pulled off the pool blanket and left it off, therefore exacerbating the problem, and letting the heat go!
I spent a few days in our pool in January and it got pretty cold at night, yet the pool was toasty warm every day, because we used the blanket when not in use! It was great to sit in the pool with a drink in hand watching the Chicago Bears game at home where it was snowing! ahh....