I've always guess-timated 20 minutes from Mizners to crossing the bridge from Poly to TTC lot (that's walking at a brisk pace, not taking in the scenery). I agree with Bio you have to know the Poly layout at night or you'll likely get lost. I imagine new GF path similar. Also you can have another 5 - 10 minutes if you're in a back Villains lot.
Been a decade since I tried to leave MK immediately after Fourth of July fireworks, but I remember that taking close to an hour to get to the car, so roughly comparable. That said, I am curious if they really let a few thousand people use this route en masse at, say, 1 a.m. on January 1. it takes you past a lot of guest rooms. Might turn into another Boardwalk situation.