Translation:Her cousin works around the clock.
Apparently, we're unable to accept answers with slashes in them, so "24/7" is out of the question.
PS: Please don't downvote legitimate questions. Not only is this section meant for questions, but you're effectively downvoting the informative answers as well. Save your downvotes for spam and misleading statements instead.
Not necessarily from midnight to midnight!
It's a colloquial expression that means they work a lot, maybe for long stretches of time, maybe during the night as well as the day. Or it could be someone on call, like a doctor, who could be working at any time of day or night, etc.