chlorine burns off in 24-48 hours. keep a 5gallon bucket with an air stone and u will always have good water on hand. Obviously if u have a large grow a larger reservoir is needed. Another alternative is a dechlorinating solution from a fish store. I use both but i have several aquariums so its on hand. I keep 10-15 gallons at 5.8 ph for my clone room and another 25gallons at 7.0ph for my soil grows and mothers.
Instead, I'd just use mycorizhals on transplant. Far more cost effective and efficient, only need to apply it once since the primary colonizer of cannabis roots is Glomus Intrardices, which takes about 6-8 weeks.