Quoting Milliseconds are Money: How Much Performance Matters in the Cloud:
5) The Proof That Milliseconds Matter …
The big guys in the cloud industry have really dug deep and proved that those milliseconds matter:
For every 100ms increase in load time of Amazon.com decreased sales by 1% (Kohavi and Longbotham 2007).
Google discovered that a change from loading a 10-result page in 0.4 seconds to a 30-result page loading in 0.9 seconds decreased traffic and ad revenues by 20% (Linden 2006).
Google Search found that a 400 millisecond delay resulted in a -0.59% change in searches/user. What’s more, even after the delay was removed, these users still had -0.21% fewer searches, indicating that a slower user experience affects long term behavior.
Another study by Google found that an extra 500ms in loading time resulted in 20% drop in traffic.
Yahoo also found that a 400ms slower page would see 5-9% more people leave before the page finished loading.
I think this answers your question.