First time playing with using service workers caching and trying to understand what is happening with WPT reported TTFB summary on repeated views - it’s very high at 1+ seconds but document loaded time is quick
see example at WebPageTest - Running web page performance and optimization tests...
on repeat view i get
Load time = 0.072s
First byte = 1.159s vs 1st view = 0.154s
Start render = 0.100s
Speed index = 100
First interactive = >0.122s
Document complete = 0.072s
Fully loaded = 1.160s