I don't think there is. The Timelines are largely automatic without the number of options available in some other charts. I tried a couple of methods but the closest I came to what I think you want was by adding a 1 second event to the end of the day using [ 'Petunia Room', '', new Date(0,0,0,23,59,58), new Date(0,0,0,23,59,59) ], which gives the timeline in the attached image, a live version can be seen at
http://brisray.com/test/dionela.htmHopefully someone can come up with something not quite so kludgy.