EA's website states:
"Status: Pre-Release Tue Mar 22 12:00:00 CDT 2011"
Therefore, I would say 12:00pm today if you live in the CDT zone in the US. That's 1:00pm on the east coast and 10:00am on the west cost.
I don't buy direct download games, but I will assume it will be a little slow since a lot of other people are going to download from EA's servers as well.