A film is usally released on DVD after four months nowadays and Sky Box office about two months later, Then Sky Movies after another 6 months or so. As for the terrestrail premiere, it used to be at least three years but now seems to be anywhere from two to three years. Take two of BBC1's Xmas premieres. Superman returns and Pirates Of The Carrabien 2. Both released in July 2006 but premiered after two years and five months on BBC1.
So to answer the OP I would say a film released in March 2008 would be as follows:-
March 2008 - Cinema Release
July 2008 - DVD Release
September/October 2008 - Sky Box office
March/April 2009 - Sky Movies
September 2010 - March 2011 - Terrestrial