Certified GKH Gardening Expert
Blood Oranges are mid season fruits, so the fruit is ready to harvest in the months of January and February.
You can check the stem of the fruit; when the stem begins to dry, the fruit is nearing harvest time.
The fruits exact ripening time is dependent on the variety and the environment. They do need the cool evenings to make the blood red color deepen.
Blood Oranges cannot tolerate freezing weather.
Here is an article with more information.