What does "a time efficient way" mean?

[PredatorTheSkullCollector]

Good day,
I've encountered this expression in one of my personal books and it made me feel embarrassed.
Oh,I almost forget this one
"Try to fit as much of it in as you can when you're younger."
I'll be grateful if you help me.

[Beeesneees]

In a time efficient way - in a manner which wastes as little time as possible.

Try to fit as much of it in as you can - Whatever the wider context is, you should try to do as much as possible when you are young (presumably because it will be harder to find the time to do it as you get older).
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Cheers m' dears!