Blocked Dates is an add-on for concrete5. It adds a new Blocked Date/Time attribute type that you can use with pages, files, users and in your custom code.  Additionally, if you have the eCommerce add-on you can use Blocked Dates with products and orders.
   
Blocked Dates provides all the functionality that the Date/Time attribute built in to concrete5 has plus it adds the following features:

• Ability to block out days of the week
• Ability to black out specific days of the year
• Ability to specify a cut-off time after which the current day is blocked
• Ability to display a Blocked Date as time only value
  (the concrete5 Date/Time attribute supports times but only in conjunction with dates).

When a Blocked Date is presented to the user (e.g. when the User registers or when checkout in with an order) a standard date field is displayed.  When the user clicks on the date a calendar popup appears - just like with the Concrete5 Date/Time attribute.  With a Blocked Date value, however, any dates that are blocked will be grayed out and disabled.  If the user hovers over those blocked dates a tooltip will appear explaining why the date is not available.
           
All of this works by just setting values in the Concrete5 Dashboard.  No programming in PHP or Javascript is required.  Should you want to use Blocked Dates in your own custom code, however, the Blocked Dates add-on does include a helper class the provides access to all Blocked Dates functionality.  It's even possible to create Blocked Dates without configuring them from the Dashboard.