Is there a way to change your timezone in Chrome devtools?

To do this in Chrome Dev tools you can use the Geolocation sensor emulation. Go to the 3 dotted menu, More Tools and Sensors.

There's a Geolocation dropdown with some common locations but you can change your preferred one as well. To do that you can choose Other... in that dropdown and enter a custom Timezone ID

Here's a demo page to test it: https://mathiasbynens.be/demo/timezone and a video that shows the procedure: https://www.youtube.com/watch?v=pIpN_AuV4AI

2020 update: see the other answer, which shows the result of a feature request I filed with Chromium to implement a way to override the timezone.

Note that the technique only works to change the location (including timezone) in that tab. Other tabs will still use the system's timezone. DevTools isn't a reliable way to spoof your timezone.

To change the timezone for all tabs in the browser (Chrome or Firefox or whatever), on Linux/MacOS, you can launch the browser with the TZ environment variable set to the desired timezone name:

TZ=America/New_York chromium-browser