I’m made out of five letters,
And I’m made out of seven letters;
I have keys but I don’t have locks,
I’m concerned with time, but not with clocks.
What am I?
A piano. The word piano has five letters, and the scale on the piano is A through G, seven letters. The piano keys don’t have locks and playing piano requires you to keep time (but with a metronome, not a clock).