I'm also very sensitive to the timing of my exercise, and I usually try to put a day of rest between exercise days. The "very tired" evenings that I occasionally have correlate with a lack of a rest day.

Last week I did two 62 milers back to back. I was pretty beat the day after the second ride.

But I would definitely do the ride.

Also, I've been riding a lot more, and there is a real change in how I feel on rides. They seem much easier. Perhaps you can accomplish that between now and Aug 17.