I think the time line is off regarding the length of time the 20th Me and 15th Al were locked in mortal combat. The 20th was just about out of ammunition and had fought back five assaults before launching its famous bayonet charge. And, after each one of those assaults and retreats, Colonel Oates would have had to expend some time reorganizing the 15th's survivors for the next attempt.
Rather than twenty minutes (1700-1720), I believe the combat lasted just under two hours; the ending coinciding with the arrival of the 12th and 5th Pa. Reserves, Fisher's brigade. Colonel Martin Hardin, 12th Pa. Reserves, remembered, "...stumbling over rocks and numerous dead of Vincent's and Weed's gallant brigades. As we advanced a few scattered shots cane from the retiring enemy" Of course, the only retiring enemy on the south-eastern side of Little Round Top would have to have been the 15th Al.
Lending confirmation to this viewpoint is the recollection of Captain Park, one of Colonel Oates' officers, who reported seeing the flags of two advancing Union regiments threatening the 15th's exposed right flank. Oates later speculated that Park mistook the fire from Stoughton's sharpshooters and the 20th Me skirmishers secreted behind a rock fence on his right for two advancing regiments. But Oates was wrong, the men behind that rock wall did not have flags with them.
Additionally, I think the arrival of the 140th New York (and Weed's brigade) occurred about an hour later than the timeline indicates.
Prior to that time, the fight for possession of Houck's Ridge and Plum Run valley by the Texans was being held up by Smith's two guns and the advance of the 40th NY and 6th NJ. When that obstacle was cleared, the 4th, 5th Texas and the 48th Al were free to start up the western face of LRT and attack the 16th Mi. Their attack would fix the arrival time of the 140th NY and Hazlett's guns on LRT.
According to Colonel Waddell, 20th Georgia, "...About 6 o'clock, a regiment was moved to get to our left flank. A shot from Private John F. Jordan, of Company G, unhorsed the officer leading when their ranks were broken, and they retreated in wild disorder..."
Colonel Egan, 40th NY, was knocked from his horse during the advance down the valley and was most likely the target of Private Jordan. Though somewhat imprecise, "about 6 o'clock" presents the analyst with a time frame (5:45 p.m. - 6:15 p.m.) with which to work and compare to other linked events. For instance, Winslow's battery was still in the Wheatfield when the 40th NY and Smith's two guns retreated through its southeastern corner. Winslow would use some of Smith's extra horses to retire five of his six gun battery. Just before that happened, Smith heard Hazlett's guns firing from LRT, indicating the 140th NY had arrived.
Attached are a few maps to illustrate the sequence and estimated times for the events discussed.
4:45 p.m. Vincent's Brigade goes into position, skirmishers advance. Hazlett's battery arrives at rear of LRT.
4th, 48th AL and 4th, 5th Texas move along base of RT while 15th, 47th Al approach summit of RT.
The 44th Al faces off against the 4th Me
5:50 p.m. Left wing of 48th Al moves past remaining companies of 16th Mi as Companies A and G of the 140th NY,
in advance of the regiment, move to attack the 48th Al. Two of Hazlett's guns start to work up to summit.
The remaining regiments of Weed's brigade resumes their movement along Wheatfield road. Colonel
Chamberlain, 20th Me, moves two companies to right of line.
6:10 p.m. Weed's brigade in position on LRT. Fisher's brigade, PA. Reserves, arrives along Wheatfield road and starts
to go into position. Hazlett's remaining guns placed in position on LRT.
7:15 p.m. 12th Pa. Reserves takes up supporting position behind 20th Me as it drives the 15th Al back toward base of LRT
McCandless' brigade moves forward with detached 11th Pa. Reserves (Fisher's Brigade) in front. The 98th Pa,
Nevin's brigade, in rear.