I recently switched from using an Ipad Mini 2 to my Samsung Galaxy S6 phone whiich seemed to work best.  However I noticed that I am getting long warming up time on first startup.  If I enter and exit a menu it usually goes right away.  Any ideas what could be causing this?

It doesn't have anything to do with the tablet.  Do a COLD IMU calibration, and you can get the warmup time way down.

Gary is absolutely dead on.......if you do a COLD calibration of the IMU it will be ready to fly in just a few seconds....less then 15.   
I did the calibration after the aircraft had warmed up (P3P), when I first got it a year ago and it would take almost a full minute to indicate it was ready to fly.  After reading some great info on the forum I did a true cold calibration and I was good to go.
Good Luck.

Turn on you AC
Take out the battery from your P3 and put them both in front of the ac vent for good 15-20mins
Some people even put them in freezer but i didnt go that far ;)
After 15-20mins you P3 should be much cooler
Connect your tablet/phone to the RC
Turn on RC and start the app
Put the battery in your P3 and turn it on and do the calibration as soon as as you can
You be happy with the results if you do everything right

Thanks for the Cold Calibration suggestion, this corrected the warming up delay.

FlyingCircles Posted at 2016-8-8 00:18
Thanks for the Cold Calibration suggestion, this corrected the warming up delay.

Be careful. Doing a COLD IMU calibration will indeed shorten significantly the warming up period at the start of your flight. But it will diminish the precision of the altitude metering by the barometer very much.
Just do the test: calibrate cold, fly your drone to say a 100 meters high and let it come down again and land: when reaching the ground or just above the baroimeter will tell you that it is still 3 to 10 meters up in the air.
Now take off again, let the AC hover for a minute and land it again, do an IMU calibration and do the same test: you will find that the barometer is now much more precise.

PhanFran Posted at 2016-8-8 05:12
Be careful. Doing a COLD IMU calibration will indeed shorten significantly the warming up period a ...

Interesting.. will have to try that.  I've always done it as cold as possible as well (without resorting to the fridge).

PhanFran Posted at 2016-8-8 05:12
Be careful. Doing a COLD IMU calibration will indeed shorten significantly the warming up period a ...

Are you saying to do the next IMU calibration at normal temperature?

FlyingCircles Posted at 2016-8-8 18:48
Are you saying to do the next IMU calibration at normal temperature?

Well, yes, actually.
What I do is IMU calibration at least at NORMAL temperature, not when the AC has just performed a long series of climbs or descends and everything including battery, motors and IMU are super hot.
So, I do a calibration at ambient temperature, the temperature the AC will be flying in a few minutes later.
When I am in a flat region, then I just take off and don't worry: once you are sure your AC is high enough to avoid obstacles, it's ok.

When I'm in a moutainous region though I power up the AC, take off, let it hover for a minute  a few meters above the ground and land it again. At that moment the ZERO - AGL point will be reset by the AC under 'normal' working temperatures. And zero will still be zero when you land after a long flight, not the so-called '3 meters' or '10 meters' while your aircraft is cutting the grass already.