You could test your theory more by making an extension like this:<extension name="test"><condition field="destination_number" expression="^1234$"><action application="answer"/><action application="set" data="time_name=soft"/><action application="playback" data="tone_stream://%(251,0,1004);loops=-1"/></condition></extension>This would produce a timer and use it for playback instead of the read stream.
If you wanted to make a timer you could use from the TDM you would have to make a FS module with raw dahdi code in it that opened a socket and clocked off of it and pushed it out to the channels like how some of the other timer modules do but I think if you are on a modern kernel with timerfd that this should not be necessary. If you are on an older platform like centos5 you could try the old -heavy-timer command line arg.