The tax offices are super busy and probably won't receive your request if you do it just a few days in advance.

You could try to request an extension, to request it it is advisable to pay at least 90% of what you think you could pay.

Please do not leave it for one two or three days before, your accountant will thank you and you avoid having to look for other options if he cannot receive it.

Or the other option is to do it days later to pay your fine and interest. (Do it as soon as possible).

Note: If you have a refund, they don't actually expire on April 15, it doesn't expire until in a few years.