72 Hour Visa Question. We are Canadian.

My wife and I (Canadian) will be Traveling South-East Asia for a couple of weeks then visiting China at the end. We have booked the following flights,

- 1 way ticket from Cambodia - Beijing (via Kuala Lumpur) Landing in Beijing on August 17 at 1:05AM.
- 1 way ticket from Beijing - Toronto on August 20 at 10:55AM.

This is technically around 85 hours in Beijing. But according to your website, it says the 72 hours starts the following day after arriving. We are not visiting any other citys, and we will only be visiting the Great Wall. So I think we will be fine with the Free 72 Hour transit. Am I understanding the rules properly?
Thank you in advance.