We used the DtD security entrance for Disneyland from GCH a couple mornings almost two weeks ago. We were down there 6:15-6:20 and were about 5th in line. Security doesn’t actually open until 7, but by that time the line is crazy long. It really depends what your goals are… To take advantage of the ridiculously short 30 minutes of early entry, I would get there well before 7. The lines for park entrance build quickly once Harbor security opens as well.
The teens went down to the paradise pier entrance around 6:45, and I believe they were first in line. YMMV of course ….