I mainly test in morning - around 9-11am depending on what else is happening around the house. Depending on the volume I need to add, I try to add at least half directly after I test and then wait till later in day and add the other half. This is assuming I am just replacing lost Chlorine due to sun and not starting from very low FC level. I follow the CYA/FC chart so, for example, if I am at FC 5ppm (minimum) and need to be at 7ppm (target) based on my CYA level. If I know we are swimming soon then I may add more in a quick fashion. You should wait 30 mins after adding Chlorine before you go swimming just to ensure circulation of the new chlorine. Most will say that you need to add any chemical at least 30 mins prior to your pump stopping. Not sure of your pump schedule but I have a single speed pump so I run it all day in the summer and it shuts off at sundown. Hope this helps.