On my last visit a few weeks ago, Sunday 30 Janury, Monday 31 January and Wednesday 2 February the parks officially opened at 8am.
I was at bag check on Harbour Boulevard at 7.30am and there were no lines to get into either park. I scanned in just after 7.30am on all days at both parks.
On My
Disneyland Main Park days, the area around the Hub, the entrances to the lands were very crowded but Main Street was not and you could stay away from the big crowds. Once the Opening announcement came on, the CM's dropped the ropes and everyone raced into each land. The Hub and Main Street cleared fast and I managed to get photos of The Castle with no people in the background at about 8.15am.
On my California Adventure Day, the same thing. No lines to get into the park, I was scanned through around 7.30am, and people were held at ropes at Hollywood Land and Carthay Circle.
It depends on where you want to be when the ropes drop / park opens.
If your goal is to be at the top of a turnstile line and be at the top of a rope line to be in the first loading of a ride, you need to get there at least 1 hour before park opening.
If you just want to be in the park for park opening and are not bothered about being in the first loading of a ride but want to take advantage of low crowds and low wait times, then you are fine scanning into a park any time in the 30 minutes before park opening or up to 30 minutes after park opening.