I ride my bike in cold weather. when gloves are on, my left hand gets numb more quickly than my right. could the tightness of my watch band (worn on left) cause circulation issues? do i need to worry about numbness that hasnt subsided after 72 hours?

It is abnormal if numbness has not subsided after 3 days. The watch band should not impede hand circulation. You should see your primary doctor first for a thorough evaluation (past medical history and social history for this symptom are important besides the examination). You may be referred to see a neurologist or a vascular surgeon if it deems necessary. Good luck.

One consideration is nerve compression over the left wrist, and your symptoms would not be unusual if you have carpal tunnel syndrome. It would be worthwhile to have your physician assess, and if persistent numbness, undergo an EMG study.