A company(financially closed as of Dec. 31, 2017) should submit the CTR(Corp. Income Tax Return) by the 2nd of April without any exception(only if in a group which need to make up those combined financial statements by the end of April).
It's around 750,000 companies in this time so you'd better to keep the due date to avoid any special attention from the NTS.
Any late filing should be fall in trouble with some penalty, and you can file it anyway from the 1st of March when you ready, but need to pay the tax by the 2nd of April.
This year NTS will try to find some expenses without a proper invoice or receipts, vehicle related expenses and abuse of corp. credit or debit card intentionally through their bigdata.
Any questions, please send me an email to email@example.com