Yep - its always a 30 minute penalty for not following the clues properly and in previous seasons they also added the time saved - so if taking the taxi took 5 minutes and walking would on average take 15 they would get (15-5 = 10 minutes plus 30 minutes = 40 minutes)
But there is no rule to say the girls would have had to tell Kevin and his dad. From a "this is a game and we need to outperormn other teams" point of view, they were smart not to tell them, but if I had been in that position and got on with kevin and his dad, I think I may fter reading the clue and learning the pit stop was really near by - so no chance of getting lost and kevin and his dad skipping past them - and I knew his dad was struggling witht he task and would take some time to finish it, I may have told them.
Kudos to the girls for doubling back, repeating a section of the task and STILL finishing in second place.