How long does a bar of Xanax close? One dose of Xanax can close everywhere from 31 hours to 134. five hours (five. or six days) within the body, they rely on elements associated with the man or woman who took it. However, the calming, relaxing, and sedative outcomes of Xanax are usually put on for approximately 8 to 12 hours. GET UP TO 20% OFF USE CODE “SALE10” Visit now: now: