Most chlorine removers work instantly, just because chlorine is a relatively unstable gas and it breaks down quickly. I know a lot of people who just add the chlorine remover immediately to tank as the water is being added. Seems to risky to my line of thinking, but if you are using a python system, then this is what you'd have to do. Since I still use the bucket brigade, I add it to the water as it is coming out of the spigot and by the time I get around to adding the water, it may have sat for 15 - 60 minutes.
Now, because chlorine is an unstable gas and does not last long in water supplies, many municipalities are going towards chloramine, which is ammonia plus chlorine and which is much more stable. If you're on public water, call your department and ask them whether they use chlorine or chloramine to treat their water supply. If it is chloramine, then you'll have to use a treatment (I use Prime) that rids chloramine.
Val