Make this by adding one volume of Chlorox to 9 parts tap water. If leave the bleach on the plates, your experiments may be killed unless there is enough dilution. Therefore I dip them in sterile autoclaved water or rubbing alcohol which evaporates faster. However for most uses the wet Petri plates are fine. In my micropropagation lab, I fill the wet plates with sterile agar which was autoclaved in bottles or jars and plant my strawberry plants.
Growth takes weeks, but very few dishes become contaminated.
Killing is a logarithmic function. You will never kill every organism in a million plates. I suggest you do a test. I let them soak 20 miuntes and I have no problems. Therefore less soaking would sterilize most plates.