Routinely, lysis of cells with hypotonic solutions is carried out along with some physical (douncing) or enzymatic (lysozyme) method to break open the cells. If one were not to do any of these and just resuspend cells in water, how long would it take to lyse the cells? I was discussing with a lab mate who claimed it would take hours while in my understanding, salt equilibrium should not take very long (maybe on the order of minutes?) and hence, lysis should be done within 20-30 minutes.
In the case of red blood cells, hemolysis in pure water occurs at just over 1 minute, 30 seconds, according to this paper. (Osmotic Properties of the Erythrocyte, M.H. Jacobs and Arthur K. Parpart, The Biological Bulletin, 1932)