What size tablets did you get? I think the newest ones are 125 mg. Since you got headaches just going to 9k, I would start taking it the morning you leave for Horseshoe Meadows. But I'd only take half a tablet twice a day. Then if you still have symptoms, increase to 125mg twice a day. Some doctors will prescribe twice that amount, but I'd not try that until I felt like I needed it.
Your 2 days at HM, and then day 3 at Trail Camp is an excellent plan. Here's hoping with that slow acclimation, and with the Diamox, you will be symptom-free.
The headache brings up another question: Do you drink more than a cup of coffee each day, and do you change that habit when you go on a trip? I found that I would get a headache any time I'd go "off coffee" when I was drinking several cups each morning. I've cut back to the half-caff variety, and that seems to help.
