I developed some achilles tendonitis on a long tour. I resorted to stretching every morning and icing it at night when I could, and that seemed to keep it from becoming disabling. If I were you, I would not ride anymore before your tour. Between now and your departure date, ice your achilles every two hours throughout the day if you can. No stretching. The best way to ice your foot is to put your foot in a bucket of ice water for 15 minutes. But it hurts so bad the first 3-4 times you do it, you might not be able to withstand the pain. After those first four dunkings, it is much easier to tolerate the ice water, and your foot will go numb after a few minutes.
The second week, alternate between heat and ice. The last two days before your departure date, apply the heating pad and try some gentle stretching(you don't want to feel any pain), and then immediately apply ice. If you aren't adverse to it, take a full dose of anti-inflammatories(ibuprofen/Advil) every day and don't miss any dosages. Then when you leave on your tour try to gently stretch your achilles every morning, and spend the first 30 minutes of your ride spinning easily as a warm up. If you feel pain when you stretch, don't stretch--you'll probably just do more damage.
You should also lower your saddle about 1 cm to protect your achilles from having to stretch too much at the bottom of your pedal stroke. For the first week of your tour, plan on taking two rest days--so two days riding, one day resting--and ice your foot as much as possible on your rest day. That will also help your butt get acclimated to long days in the saddle.
I had days were I finished, and I thought I wouldn't be able to ride the next day, but the next morning the pain was completely gone.
