I have a hard time believing the de-chlorinator works instantly ..knowing that it is mixing in the tank water with existing tank water and the new tankwater..just doesn't add up..however, I do believe it acts fast..( I guess to much chemistry in college)
keep in mind that you are actually only changing part of your water..maybe 25-30% ..in essence the ppm count of the chorine/chloramine is diluted by the existing tank water..minimizing exposure to the new chlorine/chloramine..the additive to de-chlorinate should be added to the existing tank water...to further minimize the impact any chlorine/chloramine might have.
if you are doing really big water changes ..as some breeders do..they age the water for up to 3 days before using it..
pythons make it easier to do water changes..tho I prefer to use a regular vac to clean the gravel.I prefer to dump the water from the tank on the lawn.and I notice the area that gets that water if very green...LOL