FWIW - I have never heard of an hour long potty line? I would also not bring a potty with me to WDW, we had a training potty in our van for outings and long car rides but I can't imagine using one in the parks, YMMV.
We have been with toddlers and recently trained toddlers a few times, don't worry. The only times we have found lines are right after a show, like FOTLK or Epcot shows, avoid the closest restroom or go right before and you will be fine. For example after BATB the line for the restroom between the theater and TOT is huge but if you head left after leaving BATB there is a another restroom and it usually dosen't have a line. Just have your guidemap handy and have your toddler go often.
FWIW, anytime I hear a toddler obviously in distress - mommy I need to go now - I let them go in front of me if it helps.
TJ