the bleach solution should be 1 part un-scented, straight bleach, to 19 parts water.
1 minute is plenty to kill any parasites, as well as algae spores and most snail eggs. if it's ambulia, give it a 20 second dip...this plant is somewhat sensitive to bleaching
it's then a good idea to soak in water that's been triple dechlorinated for a few mins afterwards, after rinsing in some plain tap water after the bleach dip.
I just like to be super cautious when bleaching things before they get added to the tank.