Get your taxes done using TurboTax

Ok thank you.  If I cannot send it in the second half by April 18th, 2018, would it be best to set up a payment plan, or just be late with the second half, if I can have it paid by August?

I know you can only ask for a payment plan once every 5 years or so, so I would rather just pay lump sum in August.  What are the penalties for such a thing?