When the water is chilly/ cold,  algae does not grow.  Chlorine last longer and prevents algae growth.  The sooner you open your pool,  the less  heat has time to burn chlorine out of the pool from the closing.  If the winter months were cold,  there is a really good chance the chlorine level is still good from the closing, so opening it while it’s still cold (water temp) will assure a clear blue pool and the opening chlorine will only add to the already existing chlorine.  March / April are great months to start opening pools.   Have a great season!!!