I'm thinking about this one. I think I'd wait until the hair algae starts. That's when the HA is taking advantage of the phosphate now leaching from rock and sand and any nitrate that gets past the denitrifying bacteria of the infant sandbed [which is why you let the snails and hermits take care of the tank for a few weeks before putting a fish in: fish poo is a little higher up the food chain]---ie, let the bacteria-driven ammonia --->nitrate--->nitrite---->nitrogen-gas cycle get a little more robust before adding cheato, because it will also sop up nitrate as a fertilizer, and that might impact the bacteria a bit by taking some of their food. I'd like to ask a biochemist on that one---but it's a question, at least.
Once the hair algae is going, it's going to do that anyway, so more algae will only scarf up what otherwise the HA would get. And it's a farm for copepods, which also eat algae...or at least film---so at that point, it could go in.
