based on this, it shouldn't take more than half a day under the worst circumstances (single EBS drive with crappy performance), and if you Raid together enough drives, you can do it in about an hour. Correct me if I'm wrong, but you pay for EBS by size, not physical disks, so the more you can split up your data in blocks, the more performance you're going to get.
http://stu.mp/2009/12/disk-io-and-throughput-benchmarks-on-a...