I would think that the clearance is relatively quick. Although we don't know the half-life of Arimistane, Arimistane is a metabolite of 7-keto-DHEA. 7-keto-DHEA has a half life of just over 2 hours, so if arimistane is similar to 7-keto-DHEA, then detection by a drug test shouldn't be greater than 5-7 days, if you are taking around 75 mg daily.
Who is testing you? What kind of lab is it going to? Only WADA labs would be testing for arimistane. Any other level of steroid testing likely would not include arimistane