Your first point is technically correct, but 24-hour days and 7-day weeks are a de facto global standard at this point in history. There are outliers, like the Javanese 5-day week or the experimental 5-day Soviet calendar, but they are few and far between.
To build on the good answers from superkret and nemo…
The survival Rule of 3’s says that, depending on your situation, you can generally survive:
Finding a way to stay warm and dry at night should probably be your primary concern. Hypothermia kills fast.