Scheduled post date picker selection shows wrong date in some circumstances #60195

Description

I've found an instance/scenario where, when choosing to schedule a post to publish on a future date, the date shown as the publish date is always one day ahead of the day selected in the date picker. This happens in a specific setup, detailed below.

Step-by-step reproduction instructions

1. Set your system time to GMT timezone. In my case, on a Mac, Preferences -> Date & Time -> Time Zone. Use any location with a GMT timezone, eg London, Amsterdam, etc.
2. On a test site, go to Settings -> General, and for the Timezone setting choose a city or timezone (UTC-x) in America. I've tested this with Detroit, Toronto, and Edmonton, and assuming any "Americas" city will be replicable.
3. Start a new post and try to schedule it for a future date. For example, if today is the 26th, try choosing the day as 27, or 28.
4. You will notice the actual time shown in the date picker window and the "Publish" date will be one day ahead of the day you clicked on. For example, if you click on 27, the Publish date will be 28.

So far in my testing, the "plus one day" issue happens when the system/computer timezone is GMT (any UTC + timezones, such as Madrid, work as expected), and the site's timezone is Americas (UTC with - offset) based. I've only been able to test this on a Mac.

Screenshots, screen recording, code snippet

Environment info

• WordPress 6.4.3
• Gutenberg Plugin 17.9.0, though the issue happens even when deactivated.
• MBP running Monterey 12.7.4
• Chrome 122.0.6261.129, and another report of the same happening in Firefox.

Other versions/browsers/systems were not tested.

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes