Weather widget night/day theme

I am developing a Weather Widget for an iOS app. Basically what this widget will do is allow the user to select a city and return it's current temperature and weather. The user can either refresh the widget or it can automatically update. But it also has to work offline, showing the weather and temperature the last time the user updated.

Question is, if I am making the widget change the background to a day/night theme based on the selected city's time. What would be the best approach if the widget has not been updated for 12 hrs and the temperature and weather when it was last updated and is being shown was at day time, and the current time the user is looking at the widget is at night time. Should I change the theme to night or day?