Randy you are correct about the timing.
There is actually a delay of the fly rod tip in BOTH directions. The inertia of the rod and the inertia (momentum) of the line and fly causes a delay between when you move the rod handle forward and when the rod tip moves forward. The rod and rod tip must bend to absorb the energy of the back cast before the rod tip can move forward.
The reason that it is greater with heavier flies is that they have more mass and therefore greater inertia and therefore a greater delay. It also occurs with longer casts because more line = more mass that causes the rod tip to bend before it actually moves.
Regards,
Silver
"Discovery consists of seeing what everybody has seen and thinking what nobody has thought"..........Szent-Gyorgy