I ran the motor in for about 5 mins on 12v, soon got bored of that
i wouldnt worry about it jonathan, just use it as you would and keep tabs on how hot the bearing housing gets, i still check mine now and again as im using them, its ony my high speed spindle that shows any signs of struggling and thats only if i push it to 30000/40000 rpm

phils point is confirmed as all three spindles produce less bearing heat as time goes by