Business Hour Block: Time validations are missing.

### Steps to reproduce the behavior

1. Go to 'My site > Page/Post > Add new page/post'
2. Add the block 'Business Hours'
3. Select the same value in the opening and closing time.
* What I expected to happen
It should show a validation to change the closing time to be different
* What actually happened
It let the user enter the same value for opening and closing hours.
Screenshot

4. Opening time is 1 pm and closing 9 am
* What I expected to happen
It should show some message that closing time falls on the next day
* What actually happened
It lets the user enter without any message or warning.
Screenshot

5. Add multiple slots with similar opening hours.
* What I expected to happen
Multiple slots with the same opening hours shouldn't show up and it can be validated.
* What actually happened
Multiple slots with the same opening hours show up.
Screenshot

6. Add multiple slots, on the last slot leave the opening hour blank and enter a time on the closing hour.
* What I expected to happen
There shouldn't be any comma before the hidden slot.
* What actually happened
There's a comma after the second slot on Monday because the opening time is blank on the last slot.
Screenshot

7. Enter any special character in the time input boxes.
* What I expected to happen
The input box should validate the characters entered.
* What actually happened
It lets the user add any character.
Screenshot

### Context

#### Browser / OS version
Safari/Mac OS Big Sur 11.2.3

#### Is this specific to the applied theme? Which one?
No

#### Does this happen on simple or atomic sites or both?
Both

#### Is there any console output or error text?
No

#### Level of impact (Does it block purchases? Does it affect more than just one site?)
No

#### Reproducibility (Consistent, Intermittent) Leave empty for consistent.

#### Screenshot / Video: If applicable, add screenshots to help explain your problem.

Start by reproducing the reported cases in the Business Hours block: equal times, overnight hours, duplicate slots, blank openings, and special characters. Review the block's time-input and slot-validation entry points, then verify that each invalid case shows the expected validation or formatting behavior without introducing the reported comma.

Written by the indexing model from the issue text.