I believe the 1/2 life of Xanax is 6 - 12 hours.
Half-life: time taken for blood concentration to fall to half its peak value after a single dose. . This time may vary considerably between individuals.
I agree, if your looking for longer lasting steadier levels I would go with Valium. That is my personal opinion and yes I do take Valium. I hope you discuss this with your physician.
Stay with us my friend.