I have the same issue. Actually, since TurboTax helps prepare Estimated Tax Payments and vouchers, this is a product question. I do not see a way to use TurboTax to calculate Estimated Tax Payments that vary by due date. Does such an option exist?
To your question about whether or not your Social Security will be taxable:
If your IRA withdrawal is large enough, it will increase the taxable amount of your Social Security income.
That will increase your Total Income (Form 1040, line 9), which increases your Adjusted Gross Income (Form 1040, line 11) and your Taxable Income (Line 15), and hence your taxes.
The amount of the increase can be estimated by making a TEST COPY of your previous year's TurboTax file and entering your estimates in there. This will give you an idea of the tax impact various IRA withdrawal amounts will have on your total taxes.
CAUTION: Be sure to make these "what if" changes to a COPY of your file, and not the actual live file that you filed with the IRS.
I will repost this question as a product question.
