24 hours out will allow it to come up to room temperature as well as allow any chlorine to evaporate. The original poster has the right idea.
However, that doesnt mean that the tap water is still good to use. Depending on where your water is from, it may be full of junk and minerals. You need to get a PPM tester to grow -- If you skip out on this dont ever ask for advice on anything that goes wrong with your plants here, we'll laugh at you and tell you your shoelaces are untied because its that retarded to not have a ppm meter in every grow room. The PPM meter in fresh tap water will tell you how many ppm that it has in the water. You want near zero the best you can.
If your tap water is under 100ppm, it is good and safe to use in growing.
If it is over 100ppm, then you need to use filtered R/O water to get rid of the junk in your water.
Good luck, ask anything else you need to make sure you've got it right......