Thanks to Gerhard, we've got now a new property for hosts and services : maintenance_period :)
(cf http://shinken.git.sourceforge.net/git/gitweb.cgi?p=shinken/shinken;a=commitdiff;h=f82f60196cf9a454c0eb03d6e46e8dbbeca0984c and http://shinken.git.sourceforge.net/git/gitweb.cgi?p=shinken/shinken;a=commitdiff;h=dca3de273d4da0953703d6c6547290857d02aecd)
Like it's name says, it's a way to define a period that will be a downtime for the host. It's a easier way to use it than create a specific timeperiod with exclude. And this way will create a real downtime object, so it will be easier to addons to have true states and values about the object availability.
You can see it as a re-curing downtime :)