The Fall weather is nicer, and if you go on weekdays while school is in session, it will typically be less crowded (when I lived in San Diego, I never went on weekends and rarely in the summer months).
There have been rumors all over the place about how SWGE will be rolled out. The consensus (if there is one) is that when it “opens” there will be a period of previews - invitational and/or pre-paid. One rumor I’ve heard is that you will need an advanced “fast pass” just to get into the land for at least several months… There have also been rumors of pre-paid WDW-style “Early Morning Magic” events (early admission to the land, unlimited rides, and possibly a meal of some kind starting 60 minutes ahead of regular park opening). Based on similar events for other “lands”, and the immense popularity expected of SWGE, some people are predicting as high as $500/person. One person quipped “They could charge $1000/person and they would still sell out every date within minutes of tickets release”. Sadly, he may well be right.
If it’s a “general admission” and not a reservation system then I would say 45 minutes early??? Probably more like 4 or 5 hours Some people will probably “camp out” days in advance of the opening to be at the head of the line.
One news article I read (which I think is probably the “worst case” scenario) predicted, that if there were no “reservations” and it was just general admission, opening day could see as many as 200,000 people, with 5-6 hours in line just to get into Disneyland, then lines to get into SWGE, then lines for the individual rides. The two parks have a (unpublished) capacity of between 75,000 and 85,000, which means both parks will probably hit capacity by mid morning. I don’t remember the exact figure quoted, but the DLR parking lots are thousands of cars short of the expected numbers, potentially causing gridlock in Anaheim and possible back-ups all the way onto the I-5. And I expect that it will only be marginally better at least though the end of the year.
I am facing the same potential problem with a WDW trip scheduled for early December. The WDW opening may be slightly less insane because (a) the majority of people who go to WDW are from out of town and will have booked trips before the opening date is formally announced, (b) The DLR version will have been open for 5-6 months and many of the real “fanatics” will have already been to CA, and © Disney may learn from whatever happens during the DL opening and adjust their plans for WDW.
Sorry for the negativity, but the opening of SWGE will change to DLR experience for months - or years - to come.