Rush hour really starts by 7am and again by around 3:30pm, but dies down by 6ish, I've found. I have left Disneyland at around 6pm several times to drive back home to San Diego, and experience fairly light traffic at that time.
When I drive to Disneyland during the week, I try to leave my house no later than 7am (expecting to hit traffic, but attempting to get to DL by 9am), or I wait until 9 to leave. However, traffic isn't as bad from where I live in San Diego heading north, as it is going south in the morning.
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