That's right! The availability of HD may take a bit longer than other resolutions. If you prefer to wait for availability of HD, you can upload your video as unlisted and make it public once that resolution is available. Hope this helps.
That's because processing time varies due to a lot of factors like video format, file size, Internet speed, and upload traffic. Let us know if the issue continues even after 48 Hours and we'll see what we can do.