If there are dechlorinators that require waiting ... then I don't know. I use Hagen's Aqua Plus dechlorinator and it removes chlorine from the water instantly. I just fill a bucket with water and add the required amount of dechlorinator to it. Then I mix the water well, and add it to my tank. I believe most dechlorinators should work this way
P.S. I fill the bucket with water that is the same temperature as that of my tank water.
The rule-of-thumb on untreated tap water for water-changes is to let it sit for at least 48hrs...bearing in mind though,any chemicals and metals present will not dissipate,only settle at the bottom of the container..I'd still recommend the use of a conditioner at all times.