In reply to mike.

i'm also a recording engineer, writer, and vocalist who has completed a song in 15 minutes before, full background vocals and leads. Sweet Dreas actually contains vocals pre-recorded by Rico Love so Beyonce just added her leads and doubled his vocals. Of course, this is not for everybody. The artist, producer, and engineer must be very skilled to do quality work that fast...in this case, they all were. Most of what you hear on the final song was probably done in post-editing and mixing.