When am I Required to Pay Taxes on 401k Withdrawals Converting to Roth

In early 2025, I'm planning to withdraw $50,000 from my 401k and convert it to my Roth.  I'd like to pay the estimated tax on the conversion with cash.  When am I required to pay this tax?  Can I pay the tax later in 2025 or early 2026 before the tax season ends or do I need to pay it during the quarter in which I converted it?