/update-ping/ for amp cache update - not updating

Question

Been flogging this for a few hours and cant get anything to work.

I have a page http://www.pcadvisor.co.uk/test-centre/laptop/best-laptops-for-2017-3214618/?amp

AMP cdn url https://www-pcadvisor-co-uk.cdn.ampproject.org/c/www.pcadvisor.co.uk/test-centre/laptop/best-laptops-for-2017-3214618/?amp

AMP update ping url https://www-pcadvisor-co-uk.cdn.ampproject.org/update-ping/c/www.pcadvisor.co.uk/test-centre/laptop/best-laptops-for-2017-3214618/?amp

But for the life of me i the page does not update when the ping is done via curl

curl -v https://www-pcadvisor-co-uk.cdn.ampproject.org/update-ping/c/www.pcadvisor.co.uk/test-centre/laptop/best-laptops-

for-2017-3214618/?amp

Just seems random as to if/when it updates.

The curl output doesnt show much

< HTTP/1.1 204 No Content
< Content-Type: text/html; charset=ISO-8859-1
< X-Content-Type-Options: nosniff
< Date: Wed, 29 Mar 2017 12:20:18 GMT
< Server: sffe
< Content-Length: 0
< X-XSS-Protection: 1; mode=block
< Alt-Svc: quic=":443"; ma=2592000; v="37,36,35"

So

1. am i doing something wrong
2. is the ping just a "hey google when you get around to it" type of call?
3. do other people see an immediate update when they do the above process?

Answer 1

A cache update takes a maximum of 4 minutes until it is fully propagated (it might be faster):

End-to-end latency = Z + 4 minutes, where Z = the latency of the publisher (if any). [ source ]

So if you trigger the update ping and wait for >4 minutes, then the cache should show the updated version your page.