The only one I always get under :30 seconds time is Airfield 5 to Airfield 4, the shortest distance but barely enough time and that's after years of doing them on this same map. Otherwise the rest of them are fine, you should be able to hit 430 km/h going between them no problem. About 2.5km out from the landing strip, hard bank while holding your airbrake slows you down fast enough.
Edit* Another trick I learned that's probably a bug or exploit (reported it but no answer for weeks so I guess its fine), if you go around 335 km/h at about 100m above the ground, hold shift, then press Y (keep your phone open), the plane will literally autopilot the direction you're facing. It will adjust altitude and keep your speed at 430 km/h. If you have a further drug runner location, you have enough time to take a couple minute walk while the plane flies itself to the location.