SMIL playlists may be scheduled to play at specific times and repeat intervals. This is the single greatest difference between SMIL and other XML-based multimedia markup languages.
For details please see technical specification on Wallclock.
Play at specific time each day
The following code starts a playlist between 9 AM and 12 noon each day.
<par dur="indefinite"> <seq begin="wallclock(R/2000-01-01T09:00/P1D)" end="wallclock(R/2000-01-01T12:00/P1D)"> ... </seq> </par>
A scheduled playlist MUST BE enclosed within a <par> section. If the schedule is valid forever, set the duration of the <par> to "indefinite."
The date 2000-01-01 gives a reference to a starting point in time, and can be any date in the past. "P1D" is the ISO-8601 designation for a repeat period of 1 day.
Play at a given day of week
Play between 9 AM and 12 noon on each Wednesday morning:
<par dur="indefinite"> <seq begin="wallclock(R/2000-01-01T09:00+w3/P1W)" end="wallclock(R/2000-01-01T12:00+w3/P1W)"> ... </seq> </par>
+w3 designates the 3rd weekday, or Wednesday. "P1W" repeats the schedule each week.
Play at a specific time
Play once on January 1, 2010, between 9 AM and 12 noon.
<par dur="indefinite"> <seq begin="wallclock(2010-01-01T09:00)" end="wallclock(2010-01-01T12:00)"> ... </seq> </par>
Note that "R" repeat designator is removed.