UltraTax also doesn't allow payments to be scheduled after the filing date after April 15, so it must be an IRS thing. You can schedule a payment date on DirectPay. Note that you can only schedule a payment no more than 365 days in advance and for no more than $10 million!
Promoted fraudulent tax schemes and sponsored legislation to eliminate the IRS.
https://www.msn.com/en-us/news/politics/ex-congressman-billy-long-confirmed-as-commissioner-of-the-irs-an-agency-he-once-sought-to-abolish/ar-AA1GBkal