https://www.irs.gov/payments/direct-pay

IRS Electronic Payments are accepted above.  Direct Pay is an alternative to IRS EFTPS (Electronic Federal Tax Payment System).  Direct Pay is functional most days 23+ hrs/day.  Sunday maintenance period now.

TurboTax 2019 return was accepted by the IRS and the state yesterday.

TurboTax IRS 2019 Electronic Payment yesterday, maybe the $$ payment processes on Monday. 

My notes for 2020 1040ES (Estimated tax)

https://www.irs.gov/payments/available-payment-types-for-irs-direct-pay

1040ES (for 1040, 1040A, 1040EZ)
Make estimated tax payments in advance of the timely filing of your return.

You don't have to indicate the month or quarter associated with each payment.

IRS Direct Pay won't accept more than two payments within a 24-hour period, and each payment must be less than $10 million. For larger electronic payments, use EFTPS or same-day wire.