Aging water is an old technique from the days before effective water conditioner/dechlorinator was available. Many municipal water districts are now using chloramine which is just as deadly and does not evaporate as chlorine does.
Modern condiitoner, besides dealing with chlorine (Olympia has the full complicated story, if anyone's interested) also converts ammonia to harmless ammonium and removes (encapsulates?) heavy metals.
They work on contact, so there's no reason to wait once you have added conditioner.
With well-water, unless you have a current test outlining everything in your water, it's best to use conditioner.