You are a cash basis taxpayer and you record income when it is actually paid and expenses when you actually pay them, unless you go out of your way to set up an accrual system. This is complicated to do and not easy to reverse if you change your mind. You need expert assistance if you want to change your business accounting method.
If you run your business using accrual based accounting, you recognize income when the work is performed. But also note, this would mean that if you completed a job on December 31, you would recognize the income in 2021, even if the company doesn't pay for 90 days, well into 2022. You would have to pay your income tax before you actually get the money. It's not a simple decision to make.
