It will get below 32mins if you give it enough time.
The jet engine's fuel consumption is very dependent don speed & altitude. Basically the higher you climb, the less fuel it consumes. So while you climb and accellerate in the Arado, you have less and less fuel, but as the efficency of the engines is increasing, so is the range/duration you will get from the fuel that's left.
Once you are at stable speed/alt, you will notice remaining range & time will drop again.
So, after all, there is nothing wrong
