No move it to election day. You pay your taxes right before you step into the voting booth. All of them, no withholding over the year.
And Fitz, generally it's not a good idea to file MFS. And if you owe, you need to look closer at some of the other allowable deductions and the various credits. (Deductions are worth, on average, $.25 in tax savings for every $1 in deductions, Credits however reduce your taxes dollar for dollar.) . Pump money into an IRA now, that's deductible for last year. (Full deduction if you and your wife have an AGI of less then $92,000, partial deduction if under $112,000 and no deduction if over $112,000 AGI.) Also if she's got her own business, she's got five years to show massive losses which also knocks down your AGI. Is it a sole proprietership, or Subchapter-S? Especially if she keeps meticulous books on all income and expenses.
I do hope that you have sought professional advice (Not Bloch or Jackson-Hewitt or any place that pops up like a weed at tax time), but a real CPA. And have not filed yet.