Unless you are writing date specific code or have seen this bug arise, I probably wouldn't bother. Time bugs will likely creep in regardless, for example how would you find a bug that happens one month a year? How would you find a bug once every four years? Sometimes human knowledge/experience can't be tested out of a system. All test failures probably warrant investigation of some type.
But, as a general rule, I would try to brute force or fuzz your "inputs", a.k.a data out of your control. Random numbers, dates, user input, network packets, etc. Users and environments often act in unexpected ways and you want to make sure your bug finding isn't reduced to accidentally be working on the right day! :)
But, as a general rule, I would try to brute force or fuzz your "inputs", a.k.a data out of your control. Random numbers, dates, user input, network packets, etc. Users and environments often act in unexpected ways and you want to make sure your bug finding isn't reduced to accidentally be working on the right day! :)