I am pretty sure everyone in this thread have understood the timming of hitting the ball.
The persons who still have difficulty with serving have to think of WHEN exactly do they want to pull the direction with the left stick.
There is at least 3 differents ways. I kow that cause i watch live some of my friends play (amazing romich, mazing matheja, amazing nohar and tomiltom) and almost none of us has the same technic.
Either you decide to put the direction of the ball when the players just starts to throw his ball
Either you decide to do just before the ball is hit with the racket
Either you do it meanwhile (in the middle of both animation throwing the ball and hitting it, ? ? , does that sound clear??

). I personnaly don't understand how he does this one

)
I pull the direction before my racket hit the ball. i start to move the stick towards the area i'm aiming WHEN THE ARM OF THE PLAYER IS 90° (perpendicular) from his body and stop it just before the ball arrives at its top and is hit by the racket.(so when i release the serve button)
In general, the longer you let the direction on your left stick the closer to the line the ball will be. Not long enough, it ends up in the middle, too long, it goes out, but that, i guess we all know, right?
One more thing the timing of the direction is different when you erve down the T or wide. It also changes when your heart beat goes crazy boum boum. it changes in the way that the widow of the perfect hitting point is less wide, you have to time it perfectly. But serving great serves when the heart is pumping hard is very possible.
I hope this is not too confused and it helps a bit. My poor vocabulary don't allow me to describe as well i would
