You can use a standard filter for your dates, same as any other field, which allows searching. You can also make a selection from the Selections screen when you specifically need to type in stuff, but otherwise use a date picker.
If you wanted to, you could use two variables to store a start and end date and then use a button to apply these to the date field (or apply them to your expressions using set analysis), but I'd advise against this approach - it seems much clunkier than just picking dates from a picker or using search from a filter and the set analysis option might cause poor performance.
