apparently, your withholding will not be 90% of 2021 tax or 100% (110% if AGI over $150K) of 2020 tax. if your withholding does not equal or exceed either of these amounts or your taxes less withholding for 2021 is more than $1000, you will be subject to underpayment penalties.
the first qtr estimate was due 4/15/2021, next 6/15/2021, then 9/15/2021 and finally 1/17/2022
