Hi,
Sorry I just caught this.
There really is no standard. Some gather coralline, algae, or other gunk faster than others. This sound weird but basically clean it when it needs it.
I would say in general when doing a water change if monthly, inspect the cage for growth or blockage. It may just need a quick brush, or pulled and coraline scraped. Maybe every other month pull it to check for growth or damage to the impeller.
I am a bad example but I maybe clean my wet side 2 times a year. So if you miss cleaning it one week don’t worry.