I'm not sure whether any are used here but there are actually ways to build zero-tick repeaters - they're just larger multi block configurations instead of being a single item.
https://minecraft.gamepedia.com/Transmission_circuit#Repeate...
https://minecraft.gamepedia.com/Transmission_circuit#Repeate...
See my other comment for details: https://news.ycombinator.com/item?id=20960710