Does 72hr allowance last until 23.49 on the third day?

Hello, my parents are arriving in Bejing at 12.10 on the 27th March they intend to leave on a train to Hong Kong at 13.00 on the 30th. Therefore exceeding the 72hr transit permit by 50mins.

Am i correct in telling them that the visa will actually last until 23.59 on the 30th March therefore putting them within the time allowance for the transit?

Thank you.