Your 2 member LLC will default to being taxed as a partnership unless you chose to have it taxed as a corporation. The partnership will file a 1065 and the partners will get a K-1. He can file January 1st if he likes (without the K-1), but when the K-1 comes out, he will need to amend. Or he can wait until the K-1 comes out. Since you control the LLC, you can get the 1065 done as soon as you like. Jan 1st if you like.