As far as I understand, Meursault's conditionals basically go "if the Cottonee is hovering over land, use Fire Spin; if the Cottonee is hovering over water, check for Hydro Pump, then Protect if affirmative or Heat Wave if negative". At the beginning of the action, the Cottonee was hovering over water, prompting the Monferno to wait for a hypothetical Hydro Pump. While she waited, the Cottonee proceeded to use Endeavor, which, as a contact move, required the Cottonee to hover towards the Monferno's position, and thus, over land. The question seems to be whether the Monferno can change her mind and use Fire Spin before the Cottonee successfully attacks (and also, secondarily, whether the Monferno can swap around on her conditionals to reflect the changed situation, but nobody's arguing against that). It matters because Fire Spin landing first makes it impossible to land Endeavor successfully. TrueToCheese let the Fire Spin land first based on Monferno being ahead on base speed by about 15 points.
I'm more inclined towards having Endeavor land first, being that priority supercedes speed and Monferno was using a neutral priority move while in, so to say, Wait Mode, which was engaged before the hovering terrain situation changed. Also, very technically, Meursault's commands only had the Monferno check where the Cottonee is hovering at the beginning of the action, but that's most likely not worth fussing over.