I just came across a paper titled 'The cannabinoid antagonist SR144528 enhances the acute effect of WIN 55,212-2 on gastrointestinal motility in the rat', which says that the half-life of WIN55,212-2 is 24-36 hours. The two papers it references are titled:

'Spontaneous and precipitated withdrawal with a synthetic cannabinoid, WIN 55212-2'

and

'Repeated cannabinoid administration increases indices of noradrenergic activity in rats.' 

Hope this helps!