Dorsey sent the first Twitter message at 9:50 PM Pacific Standard Time ( PST ) March 21 , 2006 . The first tweet was , `` just setting up my twttr . '' Work on the project started on March 21 , 2006 , when Dorsey published the first Twitter message at 9:50 PM Pacific Standard Time ( PST ) : `` just setting up my twttr '' .