The application is not time-crtical, but why insert a bug when you can avoid it. [emphasis added]
The tone of this sentence implies that avoidance of this particular bug is essentially cosmetic and more or less optional.
It's not just theoretically possible; it will eventually happen that successive calls to localtime occur on successive days. This will produce impossible dates (e.g., 31 April) or dates that are 'off' by a month or as much as a year (e.g., 31 Dec 2012 vice 31 Dec 2011).
But if the application can tolerate dates that are impossible or wildly inaccurate, why bother with dates at all?