File as soon as you can.
A penalty is assessed against the partnership if it is required to file a partnership return and it (a) fails to file the return by the due date, including extensions or (b) files a return that fails to show all the information required, unless such failure is due to reasonable cause.
The penalty is $195 for each month or part of a month (for a maximum of 12 months) the failure continues, multiplied by the total number of persons who were partners in the partnership during any part of the partnership’s tax year for which the return is due. (So, if you have 5 partners you will be charged $975 for each month the return is not filed.)
If the partnership receives a notice about a penalty after it files the return, the partnership may send the IRS an explanation and the Service will determine if the explanation meets reasonable-cause criteria. Do not attach an explanation when filing the return.
Additional information: Partnership Form 1065 Stiff Penalties for Late Filing – Heritage Advisors