Sounds to me like he doesn't understand, and only because you said...
This has been going on for a few days and usually only while we're doing work with the clock.
I would think if it was a discipline issue, he'd be giggling all of the time. Learning to tell time can even be frustrating and time-consuming to children who aren't struggling with issues as your ds does.
Do you know how you'd handle the situation if it is not a discipline issue? I'm not sure I have advice for you...I can just offer what the issue sounds like to me. Good luck.
"A mother understands what a child does not say."
--Jewish proverb