When does the provisional become the ball in play?

[lms]

You hit your drive, and because it is unknown as to whether it is OB, and/or lost, you hit a provisional ball.

At what point does your provisional ball become the ball in play, i.e. can you hit the provisional ball several times, and then when you find your original ball go back to playing it?

[Kilroy]

The provisional is not "in play" until you pass the point where you realistically can expect to find your original ball.

Play your provisional and keep playing it
Keep looking for your original (if you want to find it)
If you find it, it's obviously reasonable to be looking there.
If not, you are still playing the provisional.

[gbower]

You may play the provisional ball until you reach the place where the original ball is likely to be. If you make a stroke with the provisional ball from where the ball is likely to be or from a point nearer the hole than that place, the original ball is lost and the provisional is the ball in play under penalty of stroke and distance (Rule 27-1) If you fail to announce that you're hitting a "provisional ball" then the ball is in play when it's hit.

[AAA]

When Provisional Ball Becomes Ball in Play
The player may play a provisional ball until he reaches the place where the original ball is likely to be. If he makes a stroke with the provisional ball from the place where the original ball is likely to be or from a point nearer the hole than that place, the original ball is lost and the provisional ball becomes the ball in play under penalty of stroke and distance (Rule 27-1).
If the original ball is lost outside a water hazard or is out of bounds, the provisional ball becomes the ball in play, under penalty of stroke and distance (Rule 27-1).