Parts photo's always need to be approved as far as I'm aware. Generally it's done within a couple of days assuming the pictures are high enough quality. I don't think that other people's part photos do appear instantly.
If you want to see a record of the changes for a part you can scroll to the bottom of the page and click "See change log". This shows the time the photo was submitted as well as when it was approved.
It may appear that some part photos appear instantly because my husband submits some for me under his account name. My laptop doesn't have access to our scanner, so he does them and I approve them 'instantly'. Also when there are new parts submitted that say they can provide a photo, we give those photos priority.
Currently there are about 200 photos waiting for approval. We do have to verify that photos are not simply copied from other sites such as Bricklink. I've just approved your 2 photos because they didn't require much research or part corrections, but any future photos you submit will be taken in turn.