You would be better off to request the payment plan directly through the IRS instead of doing it though TT.
I agree ... #1 thing you MUST do is file timely even if you cannot pay. You can make a payment anytime you wish however you should make some sort of payment by 4/17/18. Then if you don't pay the entire balance you will get a bill from the IRS sometime in May with the balance due + interest & penalties added on ... at that time if you can pay it off then do so... if not you can make another payment and the IRS will continue to bill you every month like a bad credit card. If you have the ability to pay off the debt in the next 6 to 12 months then you are not required to get on the payment plan ... just keep paying on the bill every month. Or you can get on the payment plan at that time ... doing it online thru the IRS is easy and usually cheaper if you do the auto debit each month. <a rel="nofollow" target="_blank" href="https://www.irs.gov/payments">https://www.irs.gov/payments</a>
It is easy to do it either way.
I do want to caution you however, that IRS does charge a fee (can be waived depending on income level) for a payment plan, also interest and failure to pay penalty, so any amounts you can pay by the due date (April 17, 2018) will reduce some of the costs.
Please see below for details: