i think people should concentrate on quality instead quantity. there is nothing wrong in writing many songs, but let's be serious, where there are many, probably most of them are pretty common. my advice: try developing many storylines or musical ideas instead. it's better to come with 100 melodies and build a song from there because you will know which are the ones that worth further developing.
Also: never set a deadline for finishing a song. it should be a natural process, it will just normally flow and you will know when it's complete. don't set a deadline because you risk altering the song message just because you need to finish it more quickly.