i never bother with this, so , by curiosity I looked, and I observe the exact same thing as you!

Until Dec 29, I have a flat line at ~ 90-100ms, then all of a sudden very irregular values.

from 90 ms to 240 ms. Should I worry about this

I wouldn't worry. Also, this is Google's crawler stats, it doesn't mean visitor are facing the same changes. 240ms, is twice more than what you used to have, but it's still a good value, in my opinion.

This shouldn't have an impact on your indexing and ranking.

I understand that Google is taking in consideration the speed of your site, when viewed in Chrome, (by humans), and still, this account for very little in the ranking.

The tooth you need to look for is a sudden huge spike in googlebot crawl activity. It typically preceeds a major update and site re-evaluation

Had some trouble finding the Crawl Stats report in GSC, apparently it's now buried under Settings.

Since Dimitri noticed a similar change around Dec 29, it's possible that there's been a change on Google's end. For example, if they used to crawl mostly from the West Coast and have shifted east, moving further away from your server, that can have an effect on the average response time reported. For that reason, response time as measured by Googlebot is unlikely to be used in rankings, so don't worry about that. Unless the response times are consistently problematic, of course. But then we're probably talking 5-10+ seconds consistently.

A higher than usual response time can affect your crawl rate, because it signals that generating the page may be very resource intensive, the server is overloaded, network conditions are poor (e.g. self-hosted), etc. So then they may take a step back and crawl a little less frequently, so as not to cause any trouble.

But 90-240 ms is not bad at all, even 1000ms is probably still fine (but, as noted, may affect crawl rate). Looks like mine usually jumps around between 70 and 150. Analytics reports an average response time of 100 ms for US traffic, so that's pretty similar. That's probably the first thing I'd check if I were worried about a change in response times.

I don't see a change around Dec 29, but I have servers in various locations in the US. You use CloudFlare, but it's probably not caching your dynamic content?

Hi @Sgt_Kickaxe, thank you for your nice answer.

The tooth you need to look for is a sudden huge spike in googlebot crawl activity. It typically preceeds a major update and site re-evaluation

Precisely, as of January 21st, the Googlebot's crawl requests of my site jumped from an average of 30-40k/day to a peak of 300k/day. This week the rate is abnormally low, 2-3 k/day. I hope that the site re-evaluation is for the better :-)

On another note, as of January 13, the Average Response Time (according to GSC) the response time returned to normal levels (100-120 ms), after four peaks of 240-250 ms.