Honestly, I just toss the chlorine in once the sun's down. tried doing it in the middle of the day a few times, but it never seemed to hold. Probably because of the sun burning it off or something, especially on those hot days.
Other stuff like pH balancer or algaecide, I’ll add whenever I get to it, but for chlorine or shock, evening always worked better for me. Water stays clearer longer, and I don’t feel like I’m wasting it. Not saying it’s the only way, just what’s worked in my case.