Make Start and Due Dates, and Topic Properties in date format, available in formulas
At the moment Start and Due Dates cannot be directly incorporated into formulas. Similarly, any topic property formatted as a date or time field is simply not recognised by formulas. This is despite the fact that a number of task attributes related to Start and Due Dates such as Effort and Duration can be accessed.
The easiest way to fix this is to make Start and Due Dates available as a date number in formula Task Attributes similar to the way in which Excel can handle dates - and, ideally, using the same numbering system. A similar approach could be used to handle topic properties formatted as a date or time.