Yep, snakes do produce urates! Especially bigger ones.. My Woma python (5 ft, around 5 lbs) likes to leave biiig, chunky ones under his hides for me. Ew!
I recently read a discussion on a different forum that mentioned average for young corn snakes (not kings, but similar) seems to be 2-3 days after feeding. So 48 hours sounds about right. And, yeah, the smaller size is probably due to the smaller meal.
By your description of his behavior, it does sound like he can handle 2 hoppers, if you want to give it a try. Keep in mind that growing slowly won't hurt him (some argue it may even be healthier!), so don't be afraid to stick with 1 hopper if you feel like he does better with that.
On that note, if 2 hoppers DOES seem to be the better route for him, that means he should be large enough to move up to weanling mice with no problem. A rough average of the weights of these sizes of mice is around 9-10 grams for hoppers, 15-20 for weanlings, and 25 or so for adults. If he can handle 20 grams worth of hoppers, then you might as well move him up to weanlings once you're out of hoppers. One appropriately sized meal is generally considered healthier than multiple smaller ones, as the bones and organs are more developed and there's less hair to deal with for the amount of actual, digestible food.
Personally, I'd stick with every 7 days (so, yes, feed again on Sunday) at his age and size. You can try 2 hoppers this time around and see how he does, then go from there on which size/amount you feel is better for him.