Wow, the movie was just released in theaters on March 25th. As of today, that is only 26 days ago. I can still find theaters that are still showing it as of April 20th. In comparison, Avatar was released in theaters on December 18th. It played for a long time and it is still coming out on DVD on April 22nd. 4 months, and that was a popular movie. Less popular movies do not have a rush to be put out on DVD and can take around 6 months or more.
With that formula, I would expect to see Frozen on DVD between July and September of 2010.
Good Luck!