Do Apple Health nutrition values have per-entry timestamps?

Yes.

Yes. Per-entry nutrition timestamps for Apple Health (carbohydrates and every other nutrient type) are exposed through the meals array in the nutrition payload.

Each meal object carries:

• its own timestamp (ISO 8601, microsecond precision)

• name (food name, when available)

• type (meal category: breakfast, lunch, snack, etc.)

• quantity (amount and units)

• a full micros nutrient breakdown

The summary block (daily macros / micros totals) is unchanged, so you get both the per-entry meals and the rolled-up day totals. See the Nutrition data model.