As was said, the binding time of CYA and chlorine isn't relevant, but about 10% of the total chlorine binds with CYA per second so most of it is bound in a matter of seconds. More than 90% of the chlorine is bound in around 15 seconds (this is at a CYA level of around 30 ppm). So it's pretty darn fast and nothing to worry about. As was said, the reason for the nighttime chlorine dosing is so the higher levels of chlorine can be put to good use for disinfection and oxidation and then the next day somewhat less chlorine becomes the starting point for loss to sunlight (UV).

Richard