Does the damage-dealing layer apply before the power and toughness layer in the same timestamp?

The layer system (CR 613) governs how continuous effects from static abilities, characteristic-defining abilities, and copy effects modify a permanent's characteristics. It has seven layers (copy, control, text, type, color, ability, and power/toughness). Damage is not part of this system at all.

Combat damage and other sources of damage are instead marked on permanents as a separate game concept (CR 119). A creature's toughness is determined by the layer system, and then the game checks whether the damage marked on the creature meets or exceeds its toughness to see if state-based actions destroy it (CR 704.5g). These are sequential checks, not competing layers.

Timestamps (CR 613.7) are only relevant when two or more continuous effects in the same layer interact and their relative order matters. Since damage has no layer, timestamp order between damage and a power/toughness effect is a meaningless comparison — they don't compete in the same framework.

Concrete example: A 2/2 creature is affected by an effect that gives it +0/+2 (now a 2/4). It then takes 3 damage. The layer system already resolved the toughness to 4; separately, the game checks 3 damage vs. 4 toughness and the creature survives. There is no 'damage layer' that could interfere with the +0/+2 effect regardless of timestamps.