Using some simple algebra and
Apple's data I've estimated that Apple will reach their mark somewhere around July 19 or 20. We'll see if I'm right.
5minutes * x = 5706 songs => therefore 1141.2 songs/minute
500000000 - 494544836 = 5455164
5455164 / 1141.2 = 4780.1997896951
4780.1997896951 / 60 = 79.669996494918 hours
79.669996494918 / 24 = 3.3195831872883 days from today (July 16).
My guess is July 19th because I expect there to be an influx of downloads around that time of people trying to win the prize.