Slow time to first byte

Site: serene-wright-285300
Issue: im seeing consistent time to first byte times of 500ms+ which seems really slow. My site bundle is tiny - no JS just HTML and CSS
Here’s a picture of the waterfall:
I see this issue regardless of location e.g. tested on 5G and my home WiFi

Hi @robcalcroft,

500 ms (you shared 400ms in screenshot) is a normal TTFB on the Standard Edge Network for uncached content. We consider a range of 200 to 600 ms as normal, but you sometimes might get 100 or more then 600ms.

When I tried, I got a TTFB for 1.3 seconds, and I am expecting that happened because the website was not cached closer to my location. Once I refreshed the page, the TTFB dropped to 79 ms.