Conditional Formatting - using Time (or NOW())

Is it possible prevent depending on current time, using conditional formatting or is this VBA?

I would like to prevent a user from editing a cell (or small group cells) if the time NOW() is less than 24 hours of the time displayed in the reference cell (top cell of the column).

For instance 7 columns with a start time in the top cell, every two hours; 8:00, 10:00, 12:00, 14:00, etc. A user would be allowed to enter data if more than 24 hours but the cells become frozen or password protected form change if lesss than 24 hours.


Regards