Car freshie scent life varies with the product, fragrance, temperature, and how the vehicle is used. Some makers describe performance in weeks, but a stated duration is an estimate for that product, not a guarantee that the scent will stay equally strong every day.
A freshie in a car parked outside through hot afternoons can behave differently from one in a vehicle kept in a cooler garage. Heat can increase fragrance release, so a stronger smell today does not necessarily mean a longer-lasting product overall.
Airflow and cabin size also affect how much scent you notice. A small cabin and a large SUV do not give the fragrance the same space to fill. Different scents can seem more or less prominent even under similar conditions.
Judge the scent when you first enter the vehicle after being away, rather than after sitting with it for an entire drive. If you notice it initially but then stop paying attention to it, familiarity with the smell may be part of the explanation.
On a cold day, a softer scent alone does not prove the freshie is finished. Compare it under ordinary, similar conditions without deliberately heating it. If it stays faint over multiple checks and has already had substantial use, replacing it makes sense.
Follow the product's placement directions and keep it from contacting surfaces it is not designed to touch. Do not try to restore a used freshie by adding perfume or fragrance oil unless it is specifically sold as a refillable product.