Comcast said Monday that it is planning to make the vampire flick Twilight available to its subscribers on demand beginning after midnight on Saturday, March 21, the same day it is released on DVD. The announcement was surprising given the usual window of about three months between the release of a DVD in stores and its release on cable TV. (It is also unusual for a DVD to be released on a Saturday.) It was not clear whether the movie would continue to be available following the Saturday screening on the Comcast systems or whether it would be yanked and re-released at a later date.