There may be some relevancy to allow the casing to colonize a bit before fruiting, but SWIM doesn't generally do this. All the casing layer does is provide additional nutrients for the mycelium colony below it. I think the difference you'll see in waiting for a partial colonization of the casing layer before fruiting is larger, but fewer flushes. If you case, then fruit right away, you'll get more flushes, but they will be more sparse. Either way, if your mycelium stays healthy, you should get pretty much the same yield at the end of the day. Does that make sense?
If you let the casing colonize at a sub-fruiting temp for a while before fruiting them, I would take a stab at a 30% - 40% colonization before fruiting them. The casing will continue to colonize during fruiting as well. I suppose a benefit of colonizing (the casing) before fruiting, is that the casing layer will be more protected by antibiotics before you transition to the less sterile fruiting stage. The more mycelium you have, the less evil bacteria will be able to survive in your substrate.
SWIM does it the first way, but if you have the resources, try it both ways! Keep notes and let us know how it turns out! If THIS on continue to colonize and doesn't start pinning soon, you might want to just put a new sterile case layer on top, and continue fruiting. Too much colonization once pins have started can cause excessive aborts, simply because they are fighting for nutrients.
Peace and good luck! My mouth is watering!
-idt
