Thanks.
I though about it this at first. I might end doing something like this, but it is not yet entirely clear to me how. The problem with ranging through the participants given as arguments is to deal with all the non-lecture-info such as coffee break, lunch break, poster session, social dinner… they should also appear in the time table.
Well. This might have not answered as I wished. In particular, I understand that we cannot easily call a shortcode within a shortcode (as described above) in an elementary way. But this discussion has brought some new perspectives and way to tackle my problem. Thanks again.