temporary run times

Schedules can temporarily substitute other schedules, e.g.:
<schedule name="in_the_morning">
<weekdays>
<day day="1 2 3 4 5">
<period single_start="07:30"/>
</day>
</weekdays>
</schedule>

<schedule name="in_the_morning_replacement_1" substitute="in_the_morning" valid_from="2008-04-12 00:00:00" valid_to="2008-04-13 23:59:00">
<weekdays>
<day day="1 2 3 4 5">
<period single_start="09:30"/>
<period single_start="15:30"/>
</day>
</weekdays>
</schedule>

With this configuration the schedule "in_the_morning" will be replaced by the schedule "in_the_morning_replacement_1" for the given period of time.
There can be more than one replacement schedule for a schedule, but the replacement schedules may not overlap.
It is possible to specify only one of valid_from or valid_to in order to configure an open end or to start immediately until a certain date.