Anytime before you start motors, I do mine after I establish FPV on my smartphone, usually before home point lock, but have done after, I do not think it matters, I've seen people land, turn off motors, calibrate compass, and start motors and takeoff!
I do this: ( p2v ) (Phantom 2 Vision )
Turn on controller
Turn on range extender
Turn on phantom
Hook smartphone to wifi ( phantom-?!&@7??! )
Open app, choose camera
( CALIBRATE COMPASS )
Make sure home point established
Blinking green lights ( 6-more satellites )
Start motors
Takeoff
( have a total blast )
Get mad battery died
Go in and watch tv
( LOL ) no seriously, that is what I do ( WITHOUT ) the comic relief! Lol.
Hope this helps, but honestly anytime before motor start would be just fine!
Take care, Fly safe!
Jerry D
USA
( J Dot )