Every brand in this category claims 90 days. Here's the part they leave out.
Still, enclosed air buys the full 90: under a sink, a closed cabinet, a sealed bin, a parked vehicle's cabin. Moving air cuts it to 30 or 45: garages, attics, barns, engine bays, anywhere with a draft or August heat.
Airflow and temperature pull the oils out. A shed in July and a kitchen cabinet in October are not the same environment, and quoting one number for both is guesswork.
How to check: get close and smell it. Faded to almost nothing means spent. Look every 30 days and you'll never run a dead barrier without knowing.