B737NG Thrust Rating Question

[jetblues]

So you are sitting at the end of the runway in your shiny new NG with an assumed temperature of 38 degrees and derated 20k (22k) available.

You stand the thrust levers up and set 40 % N1, then you hit TOGA and start rolling down the runway.

At what point do you have 22k thrust delivered to the engines again ? Is it when you pass 15000ft on climb, is it on approach ? Is it never unless selected ?