Yes what he said.Ahead of time is fine. You want it to have at least a few minutes to dry on there properly anyway.
You may need to bring the target home and take some cotton q-tips dipped in rubbing alcohol to make the colors really 'show', particularly if you're doing a larger ladder and have to use some of the less contrasting colors i.e. yellow, orange, and/or combinations i.e. red/green, yellow/blue.