I've hiked with a ton of people who are susceptible to AMS and everyone them have different problems at different times. Me, I can day hike anywhere in SoCal without a problem. However, extend the time at elevation beyond 10 or 12 hours and I have had problems as low as 7,500'.
I have been taking Diamox for approximately 10 years. The benefit of the drug will vary from person to person and it may take a long time before you get a dosing regiment that works for you. I take Diamox before going above 8,500' for an extended period. Even while taking the drug I have yakked at Whitney Portal, had sleep problems above 11,000', appetite issue above 12,000' and tingling side effect problems most trips.
While taking Diamox I have gone up the mountain the same date and have acclimatized one day, both seem to work for me. Only time I acclimatized two days, I had my worst episode AMS...but this was in the pre-Diamox days.
Long story, short...I takes a while to find out what works for you.
