As far as I remember from my former BO 105 checkrides, where we sometimes practised air restarts, these 10 sec ( or was it 1 min? ) with the 250-C20 series engines relighting procedure have something to do with the rapid cooling of the compressor due to the airspeed in flight , so theres some danger, that the compressersection get stuck and a proper engine starting wouldnt be possible.
skadi