How long does one brick last?

A 200g brick typically lasts several weeks depending on cabin ventilation and how much you want the scent to project. Warmer climates and running your AC will cycle the fragrance through faster.

Where should I place this in my car?

Cup holders work best for stability and even scent distribution. You can also wedge it in a door pocket, center console, or any secure spot away from direct sunlight and heat sources that would cause it to deteriorate faster.

Will this stain or stick to surfaces?

Being a solid brick, it won't leak or drip like liquid fresheners. Just keep it away from direct contact with upholstery or dashboard surfaces to avoid any potential marks from the brick itself.