Did I understand it right?

We plan to be at a friends birthday in Beijing in March 2018. We will combine this with a trip to Japan. So we will be coming from Germany to Beijing and then we will fly from Beijing to Japan. Both will be direct flights. So we will be possible to use the 72h free transit as these are two different countries who qualify.
Correct?

We will arrive at the 16th of March in Beijing.
Did I understand it now right that we can fly anytime on the 16th of March (3 days later) from Beijing to Osaka and don't have to watch to be not over 72 hours in Beijing? So let's sey we arrive on the 16th of March at 10 am in Beijing we don't have to leave Beijing on the 19th of March before 10 am. So for example a flight that leaves Beijing at 3pm on the 19th would be also fine?
Happy to get a answer on this one and thanks in advance for taking time to answer!

>>>>>>>
Of course I meant: 19th of March:
"Did I understand it now right that we can fly anytime on the 19th of March (3 days later) from Beijing to Osaka and don't have to watch to be not over 72 hours in Beijing?"