Bilge is here too, as seayalatermoonglow. Excellent resource for those waters.
Three weeks is really pushing it - and doesn't allow for much in the way of weather window wait time....
We haven't done that trip yet, but have done the "up the outside" to Barkley Sound and back in July; beautifully rugged but long legs, high chance of fog and I really wouldn't want to do that trip without radar, esp with limited time.
I've heard "Fogust" isn't the greatest month, however we do have radar.
Three weeks is whats on the calendar but if it goes four then c'est la vie.
The current plan is July 1st departure from Sand Heads but that's not in stone. If you had to choose an Ideal time would June be better?