Spelling riddles trip you up

You could swear you’d heard this riddle at some point, but can’t fathom the answer. You try to think: a moments different then the other two as it’s not defined time... is that a clue? But what could happen in a minute but not in years, as minutes are established within years??

Blanking on anything better, you frustratingly blurt out a guess you know will be wrong. “Um... shit. Is it a clock?”

The Centaur laughs boldly. “Aww sweety, you really are just a little cutie. No, it’s the letter M”

You curse under your breath, you had heard it before, but you always forget about spelling. Reaping you’ve lost, you glance under her horse belly to see her undo the harness and release the massive Futa Centaur cock. Your face turns red, how could you ever really be expected to handle this?!

She’s still chuckling to herself. “You thought you might be witty, and your just a cute airhead. Well, time to pay the piper. I get you as I want for the ride though, so you’ll have even more fun...”