1m Android versions of Instagram were downloaded in the first 24 hours

"Eager Android users awaiting the release of Instagram scooped up a million copies in less than 24 hours.
The free photo-sharing app made its official appearance on Google Play yesterday following a pre-registration period on March 24 that captured 430,000 interested users. Instagram CEO Kevin Systrom told The New York Times yesterday that the app was grabbing 2,000 people each minute following its debut."

Source:  CNET, 5th April 2012