cant give you a time limit.... but...
from the MSDS documentation...
Stability -Moderately stable. Oxidises readily. Oxidises in air to benzoic acid. This process is accelerated by light.
Materials to Avoid - Strong oxidising agents, strong reducing agents, strong bases, alkaline cyanide solution and heavy metal salts.
Storage Precautions - Store in cool place and out of direct sunlight. Store in well ventilated area. Store away from sources of heat or ignition. Store away from oxidizing agents. Keep containers securely sealed and protected against physical damage.
Hope that helped.
-AC