What is the average time (days) for Aeration and Clarification phases of wastewater treatment, in your experience?

I am trying to understand how many days wastewater materials will be subjected to the bacteria in the activated sludge (is it enough time to complete a specific biodegradation mission a brand is claiming). Any data points from any system types (and from any countries) are helpful - I am trying to build a view across territories. Much appreciated.