The docs say that you can specify 'atTime' with a 'when' of 'midnight', but that makes no sense on the face of it.  atTime with a weekday specification makes sense, but it would also make sense to use atTime with a when of D (and an interval), which is not mentioned as a possibility.  It could also make sense to use it with other intervals (in other words, use the atTime as the starting point for the rotation calculation, instead of the last mod time or 'now').  If that doesn't work it should be stated that atTime will be ignored in those cases.  

Probably all the time related entries should be rewritten with the existence of atTime in mind, in order to clarify all the possible (and not possible) interactions.