There are a number of studies relating to this, but unfortunately I havent delved too deeply into them (most of the relevant ones appear to require payment to view).
A cursory search of anecdotal feedback gives a detection-window of anywhere from 2 to 8 weeks. Without further evidence I would recommend not taking GW, unless you have a 'lengthy' time period post-dosing prior to your event.
I should note, too, that I am unsure just how rigorous the testing you in particular may undergo, and whether your agency will even have the capacity to accurately test for GW. In saying that though, again, I would err on the side of caution (until there is strong data indicating otherwise).