No hurry. The fire's not going anywhere.
Hold your marshmallow over the fire until it's a beautiful golden brown, then pull it out. Low and slow makes the best ones.
Drag up and down on your close-up to lift your stick away from the fire or lower it closer. On a keyboard it's W and S (player 2: ↑ and ↓).
Close to the flames it browns quickly, but the middle stays cold — and hold it right in the flames and it catches fire. Blow it out quickly and you keep the black bits. Further away it browns slowly and the middle goes gooey. There's no time limit.
Watch it, not just its colour: it puffs up, goes shiny, and starts to smoke when it's nearly too far.
When you think it's just right, pull it out (Space — or in 2 players, E for player 1 and Enter for player 2). You get a score out of 100 — mostly for the colour, and a bit for a gooey middle. With two players, a breeze fans one side of the fire and then the other, and the better marshmallow wins.