Comment by sintaks

Amazon has ridiculous internal bandwidth. The costly bit is external. The time delay is largely internal buffer time - they need to pull your data out of Glacier (a somewhat slow process) and move it to staging storage. Their staging servers can handle the load, even at peak. GETs are super easy for them, and given that you'll be pulling down a multi-TB file via the Internet, your request will likely span multiple days anyhow - through multiple peaks/non-peaks.