Unfortunately, data validation in Excel itself doesn't directly support restricting data entry based on specific time periods (like dates and times). However, you can achieve a similar outcome by combining data validation with formulas. Here's how:

1. Setting Up Your Criteria:

- Identify the cell(s) where you want to restrict data entry based on time periods.
- Determine the specific time periods during which you want to prevent data entry. You can define these as fixed times (e.g., weekends) or use a reference to cells containing start and end times.

2. Creating a Formula:

- In a separate cell (hidden if desired), enter a formula that evaluates to TRUE during the restricted time periods and FALSE otherwise. Here's an example formula using the TODAY and WEEKDAY functions:

```excel
=OR(WEEKDAY(TODAY())=1, WEEKDAY(TODAY())=7) // Restricts entry on Saturdays (1) and Sundays (7)
```

This formula checks if the current day returned by TODAY() is either a Saturday (1) or Sunday (7) using WEEKDAY(). You can modify this logic to fit your specific needs.

3. Applying Data Validation:

- Select the cell(s) where you want to restrict data entry.
- Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
- In the "Settings" tab, under "Allow," choose "Formula" from the dropdown menu.
- In the "Formula" box, enter a reference to the cell containing your time restriction formula (e.g., =B1 if your formula is in cell B1).
- Under "Error Alert," choose the appropriate option (e.g., "Stop" to prevent data entry and display an error message).
- Click "OK" to save the data validation settings.

Explanation:

- The data validation rule checks the formula you created.
- If the formula evaluates to TRUE (restricted time period), the user won't be able to enter data and will receive the error message you defined.
- If the formula evaluates to FALSE (allowed time period), data entry will proceed normally.

Note:

- This approach requires maintaining the formula and potentially adjusting it if the restricted time periods change.
- It's recommended to hide the cell containing the time restriction formula to maintain a cleaner user interface.