Boysie's Bumper Fix uses toluene based resins and adhesives to make repairs to various plastic parts. The manager estimated that about $2$ litres of toluene are evaporated in the drying room $(6$m by $6$m by $2\mathrm{.}5$m$)$ over every $8$ hour shift. One day while no one was in the room to notice, the fans shut down. Workers were only alerted when the toluene sensor went off. The alarm sounds if the concentration level reaches $25\%$ of the lower explosive limit$.$ All of the products were removed to outdoors quickly by workers wearing PPE, and the fans were restarted. How long before the vapor concentration drops to $300$ppm$?$