I've been waiting like a madman...
The product page gives you the day and time of availability. If you've set your time preferences in your profile, the time is automatically adjusted to your local time. For me it's tomorrow at 2 am, or more generally, it's due to be available in PDF in about 13 hours from the time of my posting.
The "street date" of Ultimate Combat is today, the 4th, and is available from paizo.com.
The PDF also releases today, and should be available in just less than two hours.