Due to you being unable to buffer any inputs like dashing before spawning in and also a possible difference in load times, I think the timing should start as soon as you move because it would be more uniform and less of a test of reaction time of when you load into the world, also it is a lot easier to start your timer the frame you start moving rather than when the world loads in.

What I think happened was I grabbed on the same frame I hit the lava but I'm honestly not sure

Ok so I was playing the game casually bc I was gonna speedrun it after I played through the game.So I was in world 2 Hidden past and right after the first checkpoint where u need the tongue power up and I grappeled onto the thing later than I should and I went flying.but the sad part is I don't have any proof that this happened even though I swear it did