You will be asked by the purser/stewardess when (s)he passes through the cabin to ask for your meal choices. When class is fully booked you might want to approach the purser right after boarding to secure your favourite shower time. If the load is low, you should have plenty of time slot choices (depending on flight time of course).
Make sure to have the shower session ! To me it was one of the very few real treats in air travel nowadays on my way to SYD. Shower session followed by a glass of Dom and watching the morning sun rising on your video screen (tail camera view) while listening to Duffy's "Stepping Stone" in your Suite is simply a dreamlike experience
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