had my phantom for about a week and half now,i did the imu calibration when I first got it and it took ages to warm up before I got the flashing green lights, I was looking on youtube and found a video about imu calibration.in the video he said do the calibration when the phantom is cold. I put mine outside for 1/2 hour and did another sensor calibration when it was really cold. now the phantom is ready to fly in no time.. it really does work to do the calibration when cold.