4) Even at the lowest speed, trolley's progress over a considerable distance in a short time. When I figured this all out, I was dealing in milliseconds, not seconds.
This is a very interesting point. For 1/48 O-gauge, 1 scale-MPH corresponds to about 0.37" per second. As shorling points out, the minimum speed to insure reliable bump-n-go reversal varies between trolleys...but let's say we need a minimum speed of 30 sMPH. That's about 11" per second.
So. Let's say the occupancy detector (magnet/reed-switch, 153IR optical detector, insulated-rail wheel axle, 153C contactor plate, or whatever you choose) detects the approaching trolley 3" from the end-of-track. If the trolley is traveling 11" per second (30 scale MPH), that means it will pass the detector, hit the bumper, reverse, and "clear" the detector in about 1/2 second which is arguably a fairly short time!
In the case of the timer-module shown, you can indeed set the delay intervals with 0.1 sec resolution so setting what I called the 1st time interval to 0.5 sec is possible to give the trolley time to bump, reverse, and clear the occupancy detector. The 2nd time interval (how long the trolley stops) is independently settable with 0.1 sec resolution so it can be 10.0 sec, 10.1 sec, etc.
And as shorling observes, sometimes throwing in some variety/randomness can add to the fun! Once you buy-in to these low-cost timer modules, you can concoct a Lego-style combination of timer modules so the trolley doesn't stop every time but maybe every 3rd time or whatever. Or maybe a relay alternates the track voltage every 5 minutes (or whatever) so the trolley runs faster and slower. So many possibilities, so little time!