What Later just means that you don't want to watch the video as it downloads to the HDD and instead want to do or watch something else while the download proceeds. Watch Later immediate begins the download to the HDD, but will NOT immediately begin to play it back. In other words, the download ALWAYS begins immediately whether one chooses Watch Now or Watch Later. The time the content stays on the HDD varies by content. I've found Disney content has really short periods (a few days) for how long it remains on HDD and often pull that content from pretty quickly from being available to download, while other content can be on the HDD for 30 days. It is best to check how long the content will remain on the HDD as soon as it is possible to check.