Thanks for reaching out. Let's check — what device are you using to access the web app for your Nest cameras (phone or computer)? Are you using a Chrome browser? When did it start happening? Did you make any changes to your camera settings? You can try logging out, then log back into your account to see if that helps.
I am using a Windows computer. Tested on 2 different computers with Win 10.
Web browser is Chrome on both.
I have never been able to see my timezone on the web browser, so this is not something that has changed. Just wanted to check this out if it is possible to change the time zone.