I used to clean my ATS every 7 days but I have backed off of that schedule a bit. Nowadays I only clean the screens about once every 10-14 days. When I do a cleaning it is always just one half of the system too. I don't clean the box that often. I also don't try very hard to remove all the algae. Just the dark algae. I primarily gauge the need to clean by the kind of algae build up I'm getting. If it's a nice clean bright green algae, I will usually leave it alone. If the algae is dark and/or slimy, like pancake syrup covering the algae, I will clean that stuff out sooner. I don't worry about algae growing or sticking to the acrylic glass. The more algae the better if it is a healthy bright green. If I happen to feel like giving the ATS a really good cleaning to remove all that ugly stuff against the clear plexiglass, then it looks great but my water quality drops a little because there is less algae working. I have learned not to bother with it if I can help it.
On a side note, the Santa Monica ATS chamber is great for holding an inch and a half of water right up close to the lights. Just place a 1" piece of PVC pipe in the bulkhead so that the water level raises up a little. Your algae grows and floats in the water right in front of the light. As the happens, the growth rate shoots up even more. I added a second bulkhead drain to help with the drainage needs. This little customization was well worth it. With the ATS setup this way, it makes tons more algae and keeps my water quality up even better. Of course I assume that more, faster growing algae in a shorter time period translates to "better" but I really don't have any evidence. I haven't been able to get an ammonia, nitrite or nitrate reading above 0 in months and I have a happy puffer that's always pooping and 14 other fish in the tank that are all well fed daily.
Hope that helps!