... been taking 1 mg. Regular xanax 2 x daily. It has been 5 days now and I feel the Er is not effective for the full 24 hours, but rather more like 12. Is this supposed to last 24 hours or do I need 2 daily. Yesterday I took it at 10 pm but now it is pretty much worn off. It's almost 11 am. Should I ask for two daily?