The simplest way to handle this, especially if you plan on this being a regular annual event over time, is to establish a plan to file quarterly estimated taxes and it just becomes part of your annual routine. If you can pay electronically on irs.gov it's easier than mailing vouchers/checks and you can see record of your payments under you online account. Just be sure to designate the payment for Estimated Taxes and correct tax year.
If you make a one-time ES payment then you likely have to file Form 2210 Annualized Income method to show the timing and reduce/eliminate the penalty that IRS will assess by default without this method, as they assume that your income was spread out over the year. The later in the year you pay a one-off ES, the more the IRS will consider you underpaid for earlier in the year. If your income event occurs earlier in the year you're better off establishing a quarterly payment plan and keep the ES in your savings account until it is due. With the AI method you have to calculate your AGI/withholding/qualdiv/LTCG for each quarterly period (3/31, 5/31, 8/31 + 12/31 full year return) so it's bunch of extra work to calculate and file this way.
Generally - if you calculate the safe harbor using prior year tax and make quarterly estimated payments (jf needed) to meet that, then you can do a Roth conversion anytime and pay the balance of the tax required when you file. Sometimes using prior year can be an overpayment in estimated tax due during the year, but is the simplest calculation as the tax amount is known when you file (in time for Q1 ES) and not subject to running tax estimates, but you need to know how much of that safe harbor will be paid thru withholding.
If you plan on starting Roth conversions this year, see if you already meet the safe harbor based on 2024 tax then it's straightforward, or maybe it's a very small penalty to catch up quarterly ES payments, and not worth dealing with Form 2210 AI method, it depends.
See Form 2210 Lines 1-9 which show the safe harbor and penalty calculation, if you try filling this out for your situation I think you'll see how it works out.
https://www.irs.gov/pub/irs-pdf/i2210.pdf
https://www.irs.gov/pub/irs-pdf/f2210.pdf
FAQ on ES - https://www.irs.gov/faqs/estimated-tax
Form 1040-ES - https://www.irs.gov/forms-pubs/about-form-1040-es
