Does any knows how the IRS (or an other tax agency) calculates revenue?

So, somewhere down the line, I intend to run this out of my own residence. But unfortunately, there isn’t an lot of useful documentation that goes beyond the bare essentials and a really specific zoning requirement on just how much square footage that I can use for my workspace.

But anyways, my current concern is that since Epic basically pays you roughly an month late in regards to sales. I’m kind of concerned on exactly how should I report my income. Since it’s obviously isn’t an current figure of what I would be earning and that some places actually demand an quarterly filing of it.

So, would they actually care if an given payout for, let’s say, August was actually from an month or two before it or does it count for exactly when Epic pays you?