Microsoft published recently the technical document Upload Historical Data to Exchange Hosted Archive 9.2.
Although data must be shipped using a USB drive, I found this question in the FAQ very interesting:
When will my upload be finished?
The rate of upload varies depending upon the size of attachments and other factors, but it generally uploads at the rate of 40 GB per day. Large uploads are often divided up into multiple parallel uploads. In most cases, the load will begin within two weeks from the time your data and all required information is received.
This document describes how to prepare and send your historical data for upload to the Exchange Hosted Archive 9.2 service.
Use this document if you have existing e-mail that you would like to upload to your Exchange Hosted Archive service.