Does a layer 7 timestamp matter when two effects both set a creature's power and toughness to different values?

In Magic's layering system, continuous effects that set a creature's power and toughness to specific values are applied in layer 7b. When two or more such effects apply simultaneously in the same sublayer, the Comprehensive Rules use timestamp order to determine which effect wins (CR 613.7).

Timestamp order means the effect that was created most recently has the later timestamp and is applied last (CR 613.7a). Because layer 7b effects stack sequentially rather than combining, the last one applied is the one that 'sticks'—overwriting the previous value. So the later-timestamp effect determines the creature's final set P/T before layer 7c (power/toughness switching) and 7d (+1/+1 and -1/-1 counter modifications) are considered.

There is one important exception: dependency (CR 613.8). If one effect's application depends on whether another effect has been applied, dependency overrides timestamp order and forces the dependent effect to apply after the effect it depends on, regardless of timestamps. This is less common but worth knowing.

Concrete example: Your opponent controls a Humility (sets all creatures to 1/1, entered play first) and you cast Sudden Spoiling (sets all creatures to 0/2, created later). In layer 7b, Humility applies first (earlier timestamp, making creatures 1/1), then Sudden Spoiling applies second (later timestamp, making creatures 0/2). The final result is 0/2 because Sudden Spoiling has the later timestamp.

In summary, timestamp absolutely matters in layer 7b when two effects both set P/T to fixed values—the effect generated most recently wins (CR 613.7, 613.7a).