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Either or both can work. If you feel like you need to control your nerves a bit before walking out on stage, you can certainly get centered backstage. But you’ll also want to take a moment to get centered at the piano, right before playing too.
With practice, centering doesn’t take much time. Just a couple deep breaths – perhaps 10-20 seconds. If it feels like you have too much going on in those moments, the key elements are really the breathing, scan/release tension, and the auditory and physical cues (hearing what you want, and remembering the general feel of what the opening feels like physically). All of which you can do more or less simultaneously, instead of sequentially to help condense the time it takes.
Noa
