Infin, I knew that Adlerangriff was to come into force on receipt of the codeword Adler Tag, which was, I understand on the 10th, but with the attacks themselves beginning on the 13th.
Whereas Battle Of Britain day is always held on Sept 15th, interestingly as you pointed out , there was a massive attack on August 15th.This in fact represented the day of maximum effort by the Luftwaffe when no less than 1786 sorties were flown in 24hrs.
It must have been fascinating, but frightening to a small boy to have been witness to such a sight.