My 2 cents.
I have found that I can slowly pour in a dose of Alk solution in a high flow spot and by the time it takes me to close that container and open the container of Ca solution, I can pour in as many cups of Ca as needed to replenish the levels. I don't wait any time at all. It's only when the undiluted solutions combine that precipitation occurs. Also, if it does accidentally happen, the precipitate is not harmful to the tank.