Hi there Lynn,
Welcome to planDisney and thanks so much for your question!
This is a great question and the answer very much depends on your walking speed and how busy
Disney California Adventure Park is during your visit. However, in my experience with a moderately busy park at an average walking speed, it should take around 10 minutes to get from the main entrance of the park back to
Pixar Pier.
I was visiting with a group of fellow planDisney panelist friends late last year and I was convinced the fastest way to do it was to go through the
Grizzly Peak area and across the bridge into Pixar Pier. However, some others in my party were convinced it was quicker to walk around the back of
Grizzly River Run - along the path that has the entrance into
Cars Land and
Avengers Campus. I would like to note that I won our race when we tested it - though I might have been walking extra fast, but don't tell them!
I think either way is probably fairly similar. However, you do have a couple of extra options as well. If you're staying at one of the
Hotels of the Disneyland Resort, then you also have the option of entering Disney California Adventure Park through
Disney's Grand Californian Hotel & Spa, where you'll enter directly into the Grizzly Peak area.
There's also another newer entrance directly into Pixar Pier (right next to
Corn Dog Castle). This entrance can be a bit hard to find the first time from the outside, which is near the main drive into Disney's Grand Californian Hotel & Spa, so I recommend actually exiting from that area first so you can see where it leads. Again, this entrance is marked that it is specifically for Guests staying in one of the hotels of the Disneyland Resort.
With all those options, you should be able to get to Pixar Pier quickly! I hope that's helpful. Thanks again for your question, Lynn!
Have a Magical Day,
Greg