Sie können stundenlang vor sich hin arbeiten.

[GooDDmann]

could anyone help me to know what is "vor sich hin"? thanks

[territrades]

It's hard to translate, but it means that somebody works alone, undisturbed, and does not even notice how time is flying.

[mizinamo]

Agreed.

Perhaps also a bit about how he doesn't concentrate on anything else around him.

[GooDDmann]

thanks :-)