Yes, it will work. Typically, if you add a new step after a wait, leads still in the wait step will pick the new flow step when getting out of the wait step.
Be much more careful if you have multiple wait steps in the SC and you add flow steps between the 2 wait steps, while some leads are already in the second wait step. In this case, leads would go through the second wait step twice.
Finally, be cautious with removing steps before a wait step or between 2 wait steps. The leads currently waiting will skip one step.
See Wait Steps