Thirty minutes

The other day I was putting my sneakers on to go to the gym and my son asked when I'd be back.

Me: About half an hour.
Him: Is that how long you're supposed to go to the gym?
Me: It's a good amount of time.
Him: Is that because the lady in the exercise video told you?
Me: No, but that's how long she exercises too.
Him: How long is half an hour?
Me: 30 minutes.
Him: 30 minutes is a long time.
Me: It's not too long. I'll be back soon.

Pause. I actually thought the conversation was over.

Him: It's longer than 29 minutes.
That's when he flashed me a giant grin.