I believe I have to disagree about the current draw and the reverser. Of course it depends on the reversing unit. IIRC, the Aristo-Craft unit does not start the delay timer until it sees a zero current draw. I can set mine to delay at the end for about ten seconds. If I have about 25-30 feet of track, it takes longer than ten seconds to get from one end to the other. But when my trolley gets to the end, it waits for ten seconds, then starts back. If I only have six feet of track, the same setting still waits ten seconds at each end.
If the timer simply ran and reversed at each time cycle, when I have a 25-30 foot run, and the timer was set for ten seconds, the trolley would never get to the end of the line. It would stop and reverse whenever the timer ran out.
If I had a two-car trolley and the trailing car had lights, the lead car would stop when it gets to the diode, but the trailing car is still on the powered track and the current draw of the lights will not allow the timer to start, so it makes one trip and stops.
Of course it all depends on the design of the reverser unit.