I have found two citations listing the date of the action as September 27.

September 27, 1864.
–Action at McDowell’s Farm. (not in Offical Records)
- Action at McDowell’s Farm, the Richmond, VA, Campaign.

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At McDowell’s farm, on 25 [sic, 27] September [1864], the Nineteenth [2nd NC Cavalry] took the lead, and captured one officer, a Major, I think, and some prisoners. My loss in men was light, but it was here that the brave Captain J[ames]. N. Turner, of Company B, was killed, and his death was a great personal bereavement to me. He and I had served as Second Lieutenants together, and our relations were very cordial and warm, but there was unpleasantness between him and his captain, and he asked to be transferred to the Engineer Corps, which was done. After I became Colonel of the regiment, he asked me to have him sent back to it, and I remember how happy he was when he returned. He would come to my quarters every night and talk over the war memories of the past. He was commissioned Captain [9/23/64] of his old Company B, but, poor fellow, his happiness was short-lived. A few days thereafter he was shot through the head near me, in this McDowell farm fight, his sword in one hand and his hat in the other, cheering on his men. Poor, dear Turner, there was no better man or more splendid soldier.

http://civilwartalk.com/threads/civil-war-the-siege-of-petersburg-begins.100800/page-2

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Captain James N. Turner, Company D, 2nd Regiment North Carolina Cavalry, killed September 27/29, 1864 at Wyatt’s Farm [Sept.29]

Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of North Carolina