Flexible Alert Thresholds

Right now, we can only set alerts by day, week, or month. Can we set alerts through a custom number of days? For example, I'd like to know if volume to a particular eVar stayed at zero after 3 days. At the one day mark, it's too short. At the one week mark, it's too long. It'd be helpful to be able to set alerts after any number of days I want.