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It really doesn't matter. I'd take it out when you start to see nitrites, or when you ammonia gets to around 2.0... whichever comes first. Sounds like things are going good!
Give it time... it's working. I wouldn't add any more fish food. It takes a while for the ball to get rolling. I was surprised you got ammonia already - seems like it normally takes 4 days or so to show up on the test kit.
You may want to raise the skimmer a few inches if it's more than 8" -10" of water.
Is your LR in the sump above the water line? If you are not putting that LR in the tank you may want to think about breaking it up into smaller pieces for the sump.