Xanax's effects lats up to 8 hours but it can stay in your body for 2-5 days.
https://www.drugs.com/medical-answers/long-xanax-3510962/
(I have learned to check the half life of meds (and not only half life of med level in my body but in some cases, like with steroids, half life of biological effect.)

Withdrawal is the hardest toward the end in my experience. Again you can use time between doses as part of a taper once you get down to the lowest level you can- again my experience but based on a lot of research at the time.