72 hour calculation start/stop times guidance please ! :)

I will arrive Beijing at 2210 PM (10:10pm) on Sunday night from HK and depart Thursday at 12:25 (just past noon) to London. This is technically more then 72 hours, but some web sites mention calculation begins at midnight and you can leave up to midnight....does this mean I will be ok or do I need to change my flights? Thanks !