Times wise I don't really have any disagreement, though there are differences of detail. We are both reading the same report, so the broad facts seem similar enough to me. I should point out that there are actually three contemporary reports relating to the attacks that day, none of them fully correlate and Boyds timing does seem a little off when compared to the more contemporary reports of the time. Boyds report was not finalised until 11 days after the attacks, so he was working from quite old memories by then.
Its the interpretation of that data that makes it interesting.
The important question in the context of this discussion is whether Sea Hurricanes instead of Fulmars might have done better. it depends if they could get into action or not. The first hits were indeed at 12:38 (according to Boyd, about 2 mins later according to the other contemporary reports), and the fact they achieved so many hits in such a short space of time is revealing in itself, and the very point of it. They achieved that many because the fleet at that moment was defenceless. Exactly where each of the elements of the CAP were is revealing and telling of this situation. There were already 4 in the standing patrol at 12:34, and another 5 were scrambled once Cunningham gave the order to do so. Of these 4, 2 had chased the SM-79s too far, expended their ammunition and were returning to the carrier. These were the only guys to get into action against the Ju87s at the heights above 7000 ft, and then only to make threatening passes because they were out of ammo.
the others, as you say had only 4 mins to gain the height they needed, and at 1200 ft per min, that puts them at a maximum height of 3600 ft before the first bombs were dropping and a maximum theoretical altitude of 7200 feet at the end of that critical 12 mins,
Exchange the Fulmar for hurricane MkIs using the climb data I got from this site.....
Hurricane Mk I Performance
and in theory at least those hurricanes could be at 5000 feet in 1.89 mins and 10000 feet in 3.63 mins... That means that in theory at least the hurricanes could have reached the form up height of the Ju87s, and be engaging from some distance from the carrier (because of the greater speed of the mount) than the fulmar equipped unit could ever hope for.
A more realistic what if outcome is that the Hurricanes reach the 7000 ft final aiming altitude an start to engage the Stukas from that point. A big part of the stukas success that day is that the main body could circle from a safe height without interference whilst one stuka at a time descended to the 7000 foot height, took time to line up, and then delivered each attack with absolute precision. Put even a few hurricanes at either of those altitudes, and the attack is going to be completely disrupted. Unquestionably.
This very outcome was achieved 9 days later whilst ILLUSTRIOUS lay helpless in Malta harbour. 43 stukas attacked her, coming in at a height that was above the effective height of the flak curtain that was by that time in place around the carrier. The Ju-87s again attacked the ILLUSTRIOUS, the only difference being that this time the carrier was stationary (a plus for the attackers), had better flak defence (a big plus for the defenders, but it should be noted the flak was ineffective at the heights that the attacks were carried out), weather was better for the attackers...... and just 6 Hurricanes (and 3 Fulmars) that were in position and ready to defend the carrier. At least 10 ju87s were shot out of the sky, and the attackers were limited to a single hit, reflecting the greatly diminished accuracy of the bombers. Maybe these results were affected by sheer dumb luck, but at least the possibility that the hurricanes made a difference on that second occasion needs to be considered. For me, it is proof enough, just a few well placed fighters can be critical in the defence of the fleet, not because of the number of enemy destroyed, but because of the effect on bombing accuracy. Of course the density of the flak also has an effect in this equation.