On my engines I find the delay virtually undetectable. Flypaper is correct IMO about this being one of the basic laws of hydraulics which would apply to a liquid fuel line. If it was in a gaseous state, that could be another matter. Any delay seen may just be that needed for the crankshaft to achieve the new speed due to flywheel effects.

When you are dealing with a fluid in a closed line you need to think of it like a solid object, such as a stick. When you push or pull on one end, the other end is going to mimic the movement without delay. To expect otherwise is not logical to me