Start render optimization takes place before the first content appears to the user, and is critical for good HCI feedback. A fast start render time gives the user visual feedback
that the web server is responsive. Ideally you want a start render time (and useful content
display) of under 1-2 seconds (see Website Optimization Secrets for details). The start render (the time it takes for the first visible changes to appear) is composed of Time to First Byte (TTFB) connect time, server response time, processing objects in the HEAD of your document, and initial page parsing and rendering. Optimizng your start render time is a matter of optimizng each of these delay components.
time to first byte
Diagnosing Slow Web Servers with Time to First Byte – slow server response time to first byte metric – Speed Tweak
Although 80% of web performance problems are typically due to front-end issues (Souders 2009), back-end bottlenecks can slow your site down to a crawl. One thing to watch out for is when static pages load relatively quickly, while dynamic pages load slowly. This article shows what to look for when a server slows down a web site.