You don’t want users staring at a white screen. Confirm that Start Render time is within 2.01 seconds. (Please remind me to justify this number I am now offering as a rule of thumb with no explanation.)

WebPageTest.org can tell you Start Render time as well as a lot of other useful information. Waterfall charts — which WebPageTest.org will generate for you — indicate Start Render time as a first vertical line, usually blue.

If Start Render time is greater than two seconds, you will need to optimize.