Not sure if I understood you completely, if you got a field list box of type date (like month for example), you can multiselect the month values (e.g. June to September). This should result in a date range selection for your objects.
You could also use the search to set the date range, just use the search icon of the list box or click the caption and start typing (the search string is depending of the data type).
If you explicitely want to use two kind of input fields set the date range, you could use two input boxes preset with the date field data. The selected values are assigned to variables then and you can then use the date range for limiting dates in expression etc.
P.S. Could have some not-so-complicated expression if you don't have a requirement that selection of a date won't affect your data range and vice versa, i.e. of you select a date range and the select a date from the field box, it won't matter if the new selection will override your date range selection.