You can put a movie on a disk for backup purposes, but you cannot create a video disk that would be playable in a DVD player.
As to download time, that will vary depending on the speed of your Internet connection and the size of the movie. A two-hour HD movie can take as much as six hours on a 1 megabit-per-second connection.
http://support.apple.com/kb/HT1577
Regards.