On Friday evening (JST) I was reviewing the website of a company dealing with currency trading. No problems. On Saturday morning try I go back to the site, but both Chrome and Safari say they don't trust the security certificate. I checked it and the validation had expired. Odd that.
Then this morning, I visited the site again and the certificate is valid and I can get in (on both Chrome and Safari)
Then I noticed a quirk.
With the failed certificate, the notice said the certificate expired Saturday Aug 13, 2016 at 8:59:59 JST.
But with today's valid certificate the notice says the the certificate is valid from Aug 13 2016 00:00:00 GMT.
I did a check of the time difference and 8:59:59 JST is 23:59:59 GMT (note: the UK is on summer time)
Is this a problem with how browsers check certificate validity? Do they always assume the expiry time is 23:59:59 and the validity time is 00:00:00, but never check if there is a time zone difference or a summertime difference?