I suggest you follow the convention of the [`assertAlmostEqual`](http://docs.python.org/2/library/unittest.html#unittest.TestCase.assertAlmostEqual) function in the unittest module: allow for a `delta` argument in the function signature, so that callers can specify how much difference is acceptable. You may also want to check out this recipe: http://code.activestate.com/recipes/577124-approximately-equal/

I do think that having a function like this is a good idea, and it may be clearer if the function call specifies that the two datetimes can have a maximum delta of one second, or something like that. Without that, people reading this code don't necessarily know what "almost" means.