I've been on the Pacific Cup board of directors, and there are four main factors that determine the July start date and time:
1) Our guess as to the state of the Pacific High -- how soon is it going to move north and focus?
2) The tides (currents) at the Golden Gate Bridge -- we like a slack, or at least not extreme
current for the start.
3) The phase of the moon -- it's nice to have a well-lit moon in the sky.
4) Participants and families summer
vacation schedule.
These often conflict, and the
race starts are staggered over five days or a week (depending on the mix of boats), so we do the best we can.
I guess my point is that the
race start date selection may not use the same priorities as you would choose.
Finally, unless the hurricane season was getting off to a noticeably early and dangerous start, I would have no qualms about leaving for Hawaii in June or mid-July. In June you may have to sail further south, or do some serious motoring (because of the Pacific High). It's a great trip and I highly recommend it.