unid := @if(
            rndno = @Elements(unids); @SubSet(unids; -1);
            rndno = 1; @SubSet(unids; 1);
            @SubSet(@SubSet(unids; rndno); -1));
"[[http://host/db.nsf/" + unid + "?OpenDocument";

There's a way to set the timeout of the page... this code shoul be used in the pages that you are displaying.

On the body tag set the onLoad this way:
onLoad="setTimeout('location.href=<url>', seg*1000)"

where <url> is the url for "launch" form... and seg is the number of seconds of the refresh.