How to specify a specific date in an action condition ?

[alixen]

Hello,

We are using "Time period" to send alerts to specific email addresses during week-ends and it works (we use "6-7,00:00-23:59").
We would like to extend it to holidays but we haven't found any way to define a specific date.
How can we define a time period for Christmas (12/25) or New Year (01/01) ?

Thank you
Alixen