The solution eludes me. I have no doubt that a simple, elegant method exists, but I'll be damned if I can figure it out.
Very simply, I am creating a "traveling strobe" effect by incrementally positioning a luminance plate. As the plate moves, some bulbs go ON and others go OFF. This animation has a natural starting point, but it eventually reaches a state where the luminance plate needs to return to where it was at frame 24--not frame zero!
The familiar "repeated" switch cannot be used here, because LW assumes I need to repeat frames 0 through 36. How does one loop a specified range of keyframes?
I didn't find the right solution from the Internet.