Once published, it may take 5 to 10 minutes for your video to appear on Facebook. Keep in mind, the larger the video, greater the publishing time. Facebook will notify you when the video is ready for viewing.
Note: Facebook does some additional compression on the videos, so playback is a little easier - but your HD file is then played in a lower quality. You can try changing the video settings to "HD if available", so it doesn't go directly to the default - but there's still no guarantee Facebook will not compress the video. You can also try uploading the "low" or "medium" quality versions, which may sound strange, but might load better on Facebook's site.