|I usually get it within 12 hours of contact though I know it can take a few days for some. Ivy block lotion is good if you're gardening in suspect areas. I react to indirect contact with the oil so I have to wash my gloves and gardening tools after I garden. If I think I've been in contact, I scrub myself immediately with rubbing alcohol and then wash. If I get it, I usually need steroids.
If any of the poison plants get burned, you can have a reaction. If the plant is dead, but there is even a stick left, the oil can be a problem for up to 7 years and you'd never even know it's there.