That's not how it works. It's a 30km/h speed limit for one kilometer in your local neighbourhood until you hit the first through road, then it'll be 50km/h / 60km/h / 80 km/h / 120 km/h as usual, and another one kilometer at 30 km/h at your destination.
In other words, it's 2km at 30km/h plus 48km at 80km/h, versus 2km at 50km/h plus 48km at 80km/h. That's a difference of 1 minute 36 seconds.