Just open your petroleum jelly, toss a cotton ball in there, and cram it into the jelly until the whole thing is covered. You don't need to wait or anything like that. The idea is that you pull out your PJ covered ball and pull it apart enough to expose some of the dry cotton (better for lighting). Then you just light it.
They actually work so well, that after you're done playing with them and seeing how they work, I suggest just pulling off a portion of the ball and saving the rest. PJ on cotton burns long enough that just a small piece is usually plenty to light your tinder box and start a full fire.