How long ago and in what part of the year did Mae Tuck ride to the wood?

Mae Tuck and her husband, Angus Tuck, return to the sleepy village of Treegap every ten years.  The couple always heads back toward Treegap during the summer.  Specifically, Mae and Angus head back on August first.  

And so, at dawn, that day in the first week of August, Mae Tuck woke up and lay for a while beaming at the cobwebs on the ceiling. . . "Anyways, it's ten years since I went to...

Mae Tuck and her husband, Angus Tuck, return to the sleepy village of Treegap every ten years.  The couple always heads back toward Treegap during the summer.  Specifically, Mae and Angus head back on August first.  

And so, at dawn, that day in the first week of August, Mae Tuck woke up and lay for a while beaming at the cobwebs on the ceiling. . . "Anyways, it's ten years since I went to Treegap. No one'll remember me. I'll ride in at sunset, just to the wood. I won't go into the village. But, even if someone did see me, they won't remember. They never did before, now, did they?"

It's possible that the above quote is not enough proof, since a reader might think that it might be ten years this time around.  But the text mentions several times that the Tuck family gets together at the spring in Treegap, during the first week of August, every ten years.  

"But they come home whenever the spirit moves, and every ten years, first week of August, they meet at the spring and come home together so's we can be a family again for a little while."

The above quote is spoken by Mae and the "they" that she is talking about is Miles and Jesse Tuck, her two sons.  It has been 87 years since the Tuck family drank from the magic spring water that gave them immortality.  The family had to separate themselves and move away in order to avoid suspicion, but every 10 years during the first week of August, they get back together for a family reunion.