Thanks for the quick reply. The person must misunderstand because he is saying that he is authorized by the IRS to make a contribution for 2017 now (and up until October 15, 2018).
I know for an IRA contributions can be made up until April 17 and that for a SEP IRA contributions can be made up to the date of a timely extended filing, but I did not think an employee, even if a shareholder, could after 12/31 want a deferral. It seems like that would be a hassle to have to correct W2s, as well as hold off on the tax return filing.