As a pool owner, the times of year for opening and closing your pool are entirely up to you. However the “pool season” as defined by the industry is typically between Memorial Day and Labor Day. Many pool use this definition as their way of knowing when to open and close their pools.
This is by no means a strict rule but more of a general guideline that people can use. Some pool owners opt to open their pools earlier in the spring, and close it later in the fall. They can do this because they either live in an area that stays warm longer or they have a heater that is powerful enough to keep the water warm in cool ambient temperatures.
As a pool owner you just want to make sure that your pool is closed before your area reaches freezing temperatures. When water freezes it expands and if it expands inside of your swimming pool plumbing components it can cause a lot of damage. To avoid the potential for this to happen many people wait until after Memorial Day to open their pools, and then close them down again by Labor Day.
I always recommend having a pool professional do the actual opening and closing of your pool, or at the very least the closing part. It is recommended for a couple of reasons. First, they tend to know exactly what they are doing. There can be quite a few steps in the process of closing a pool and if even one small step is missed the result can be dramatic. The other reason is that many pool companies will guarantee their work. This means that if anything does happen over the course of the winter, they will be the ones who correct it. If you were to close your own pool and something happened then the responsibility to fix it would be yours. Depending on what happens that responsibility can be very costly.
In my opinion the best way to avoid any sort of mishap with your swimming pool over the winter is to make sure it is opened on or after Memorial Day, and closed on or prior to Labor day. I understand that we generally have warm days outside of that range, but like I stated before this range is more of a general guid line. Also it is always best to have a swimming pool professional actually do the opening and closing of your pool to ensure that everything will get done the way that it needs to in order to survive the winter.