I want to know the answer to the following question:
When do contestants start singing two songs?
All the background I'm provided with is that "Each finalist performs songs based on a weekly theme which may be a musical genre such as Motown, disco, or big band, songs by artists such as Michael Jackson, Elvis Presley or The Beatles, or more general themes such as Billboard Number 1 hits or songs from the contestant's year of birth.". Is that enough to answer the question?