It is normal. However, there is a trick to avoid it (do at you own risk).
I call it "The Refrigerator Trick". It sounds crazy, but it works. I put my Phantom 3 in the fridge and let it get nice and cold (for maybe half an hour). I then take it out, turn in on, and immediately do "Full IMU Calibration". It runs the calibration. Next time you start up, it should not have to sit and "Warm Up" for a long time. For me it is Ready To Fly virtually immediately.
Another (unconfirmed) positive side-effect is that it seems that it holds the horizon more level more of the time when doing full IMU calibration that way.
Good luck.
PS: I've heard some people do it by running the AC in their car at full blast with the Phantom in the car. That might work too. I've not experienced any condensation problems by using the fridge - but that might vary depending on humidity where you are.