Acid malt can take up to 30 minutes to work. When the German brewers use it, they do an acid rest at 35C for 30 minutes check the pH, if it's not where they want it they add acid malt and then wait until the pH has fallen to where they want it.
It is not appropriate for reducing high levels of alkalinity . . . I can detect lactic acid in a beer at 6 ml In 50L of liquor so it's taste threshold is not as low as some make out!
Lactic acid has bugger all effect on hardness. In fact the only acid that has an effect on hardness is phosphoric, and only when there is a high level of alkalinity
I have said all along that CRS is not a magic bullet for alkalinity adjustment, especially when you have high levels of alkalinity, you are much better off using hydrochloric or sulphuric acids individually or combined to get the alkalinity where you want it. Do that and the mash pH falls where it needs to be.
Blindly swapping acids one for another on the basis of the results of a spreadsheet or Web app is not water treatment it's witchcraft!