I don't know what the service recommendation is. I check mine when the boat is hauled. The one in the pic was in the boat when I bought it. So it's been in the pump since at least 2006 and 150 hours. Considering how the PO treated the boat, I would think the impeller is much older.
Anyway, after running marine antifreeze through the raw water, I pulled the cover off the impeller and took a good look. I could see that the rubber was starting to crack. I pulled the impeller and I'll install a new one in the spring.