Hi Dan,
You can use variables in XPath. If you have the date in a variable e.g. "BeginOfDecemeber" you could write
[CaseDate >= $BeginOfDecember]
-Andrej
You can use the answer just like Andrej said. And you can create that variable through "addDays([%BeginOfCurrentMonth%], 1)". This way you get 2/12/2017 as a date.