Streaming +30 secs is enough to count as 1 stream.
Also, if you save the song (Spotify Premium), every play still counts to the official streaming count.
Source: SPOTIFY https://community.spotify.com/t5/Help-Accounts-and-Subscriptions/When-and-how-does-Spotify-count-songs-as-quot-listened-to-quot/m-p/952243/highlight/true#M120586