Editor: Incorrect save button label when toggling dates to schedule a post

[Mamaduka]

I noticed a strange behavior of the "Now" button. It resets the time to my machine's time instead of the timezone set by WP, which can lead to strange scheduling behavior.

Example:

1. Open a draft post and switch the publishing date to the future.
2. The save button changes the label to "Schedule."
3. Switch the date back and the save button label will be restored to "Publish."
4. Click on "Now" and repeat the same steps.
5. Notice that the label isn't reverted to "Publish."
6. Click "Now" again and the label is reverted, even though the time =< current time.

I'm not 100% sure what the intended behavior should be here, but initially, I thought it was a bug caused by the update and had to re-test it on the trunk.

Screencast

CleanShot.2024-03-28.at.12.35.54.mp4

Originally posted by @Mamaduka in #60163 (review)

[tyxla]

As also mentioned in the initial comment, this could be related to #3036.

[Mayank-Tripathi32]

In the publish-date-time-picker component, there is an issue where clicking the "Now" button returns null, which creates an inconsistency with the DatePickerComponent. This causes the datepicker to incorrectly set dates in GMT format.
Current implementation:

	<InspectorPopoverHeader
				title={ __( 'Publish' ) }
				actions={
					showPopoverHeaderActions
						? [
								{
									label: __( 'Now' ),
									onClick: () => onChange?.( null ),
								},
						  ]
						: undefined
				}
				onClose={ onClose }
			/>

The proposed fix addresses this by passing the current datetime instead:

	const handleNowClick = () => {
          // Both TimePicker and DateTimePicker expect full ISO datetime string without timezone
          const now = new Date().toISOString().slice(0, 19);
          onChange?.(now);
    };

This solution resolves the intermittent datetime parsing issues that were occurring when the datepicker processed updates.

I will be opening up a PR for review

[t-hamano]

The proposed fix addresses this by passing the current datetime instead:

I don't have a deep understanding of the background of this issue, but I have one concern if we adopt this approach. For example:

• A writer presses the "Now" button at 9:00. The internal publish date will be updated at 9:00.
• The writer starts writing an article. Time passes and the writer finishes writing the article at 9:30.
• The writer presses the "Publish" button.

In this case, the writer would expect the article to be published at 9:30. But won't the actual publish date be the time the Now button was pressed, i.e. 9:00?

If so, this doesn't seem to be the expected behavior.

[Mayank-Tripathi32]

The proposed fix addresses this by passing the current datetime instead:

I don't have a deep understanding of the background of this issue, but I have one concern if we adopt this approach. For example:

• A writer presses the "Now" button at 9:00. The internal publish date will be updated at 9:00.
• The writer starts writing an article. Time passes and the writer finishes writing the article at 9:30.
• The writer presses the "Publish" button.

In this case, the writer would expect the article to be published at 9:30. But won't the actual publish date be the time the Now button was pressed, i.e. 9:00?

If so, this doesn't seem to be the expected behavior.

That does seem to be an issue. I agree that it should set the date-time to match the actual time of publishing. I'll explore alternative solutions to address this properly. Thanks for pointing it out!