Longstreet and McCall each agreed on a time that the fighting commenced earlier.
It is well established (and in Longstreet's autobiography, amongst other places) that there was no planned attack, and that Jenkins misunderstood his orders to advance the Palmetto Sharpshooters and snipe the Federal gunners, and instead charged:
"Near the battery from which the shots came was R. H.[Pg 135] Anderson’s brigade, in which Colonel Jenkins had a battalion of practised sharp-shooters.
I sent orders for Jenkins to silence the battery, under the impression that our wait was understood, and that the sharp-shooters would be pushed forward till they could pick off the gunners, thus ridding us of that annoyance; but the gallant Jenkins, only too anxious for a dash at a battery, charged and captured it, thus precipitating battle. The troops right and left going in, in the same spirit, McCall’s fire and the forest tangle thinned our ranks as the lines neared each other, and the battle staggered both sides, but, after a formidable struggle, the Confederates won the ground, and Randol’s gallant battery. Sedgwick’s division reinforced the front and crowded back the Confederate right, while Kearny’s, reinforced by Slocum, pushed severely against my left, and then part of Hooker’s division came against my right. Thus the aggressive battle became defensive, but we held most of the ground gained from McCall."
- James Longstreet, From Manassas to Appomattox, pgs 134-5.
I constructed the timeline and order of events from general observations, thus:
1430: Meade and Seymour become aware that rather than being in the rear behind Kearny, they are actually the front line. They start placing their commands into battle order.
1500: Meade leads the 1st and 3rd Reserves out to form a skirmish line and encounters the 3rd Virginia Cavalry, advancing ahead of Longstreet. Over the next hour Longstreet's division will come down the road.
1600: Longstreet believes he hears Huger's guns and orders Jenkins forward to suppress the enemy. Jenkins advances to the nearby tree-line pushing back the 1st and 3rd Reserves who were out as skirmishers. He brings up his brigade battery to shell Cooper's Battery (opening fire at 1630), but loses the firefight. Featherstone's and Strange's brigades are only just coming in from the march and are going into camp routine.
1645-1700 (Jenkins' first charge): Jenkins charges his brigade at Cooper's Battery, which is defended by the 1st and 9th Reserves. Cooper's battery was held and Jenkins repulsed in disorder. At 1700 Longstreet tries to recover the situation by sending orders to Kemper, Strange, Pryor and Featherstone to attack. Wilcox received no such order. Kemper's brigade (and probably the others) were in the middle of cooking their dinners, and were not ready to make an attack.
1730-1800 (Kemper charges the German batteries): Longstreet started issuing orders to support Jenkins by attacking at 1700. Kemper went in south of Jenkins at the junction of McCall and Hooker, and charged 2 German 20 pounder batteries (from the arty res) supported by only 6 coys of the 12th Reserves. The Pennsylvanians fell back out of range and McCall sent the 5th, 8th and 13th Reserves down on Kemper's left, and Hooker sent Grover's brigade at Kemper's right. Realising he was now about to be in a Kesselschlacht, Kemper withdrew, taking 414 casualties in the process of whom 165 were captured by the 10th Reserves charging their rear. At 1740 Wilcox saw Strange's brigade advancing, and on his own initiative started getting the troops in order.
1800-1815 (Jenkins' second charge): Jenkins rallied his brigade and, with the 9th and 10th Alabama of Wilcox's brigade, charged again. Cooper's Battery again was held. The two charges cost the Federals 258 casualties, and the Confederates lost 802. By this point, Dana's and Sully's brigades had returned and were behind McCall solidifying a second divisional line behind his.
1800-1830 (Branch and Strange go into the Kessel): Branch was on the right of Kemper, but was delayed. Strange (Pickett's Bde) followed Branch. Strange came up against Hooker's division, which they only engaged the skirmishers of Hooker before retreating. Branch got hammered by the 5th, 8th and 10th Reserves, and pushed them back, gaining 2 abandoned 20 pounders. Sedgwick's men countercharged and repulsed him. Strange came up against Hooker's division, and were repulsed.
1815-1845 (Wilcox's left charges Randol's battery): The left of Wilcox's brigade, the 8th and 11th Alabama, launched a charge at Randoll's battery, left of Cooper's battery and in Meade's front. They charged the 4th and 7th Reserves, and were initially repulsed. This was apparently not a planned attack, but the CO of the 8th Alabama, seeing the 9th and 10th charging with Jenkins, launched of his own accord. Running into 12 guns (as Thompson's battery also engaged) and 2 regts, the 8th Alabama was repulsed by artillery alone, and then the 11th. Parts of the 7th Reserves then countercharged, blocking the artillery's arcs. The Alabamans turn and received the 7th Reserves (capturing large numbers of them), and use the fleeing Pennsylvanians to mask another charge on the battery, which was overrun. However, out in the open the troops on the battery were shot down and forced to retreat for lack of supports.
1845-ca. 2000 (Pryor and Featherston demonstrate against Kearny, joined by Gregg): Pryor moved to within skirmishing range or Kearny's division and thought better of making a charge. Featherstone would form on his left, and later Gregg would move in to support. No assault was made on this front.
1930-ca. 2000 (Field captures Cooper's and Randol's Batteries): Ordered to the front about 1900, Field deployed his column where Jenkins had been. McCall had identified that his line here had been battered to non-existence, and had tried to get Berry to fill it. However, the martinet Kearny had quashed all the initiative in his subordinates and despite seeing the hole, no-one was authorised to move to fill it until Kearny approved. Kearny was eventually found and approved, but it was too late. Heintzelman had seen it, and had Taylor's brigade move there from Slocum. Caldwall's and Meagher's Brigade arrived from White Oak Swamp Bridge, and were placed behind Kearny. Palmer and Howe's brigades, under McClellan's orders, had marched to the crossroads and were behind Hooker. The entire position was solidifying. However, before Taylor could plug the gap, Field charged and overran the guns. He could not advance any further though as McCall's men supported by Sedgwick's right held the woodline. Field fell back to the next woodline, and JR Anderson came up and they solidified their position in the woodline with the abandoned guns between the lines. To the right of Field, Pender had advanced against the German batteries, but found Sedgwick's division defending it. To his right Archer found Hooker's division. It was dark and neither attacked. In the dark McCall blundered into Field's brigade and was captured.