You can treat date fields as special number fields that count the number of days that have elapsed since some arbitrary very early date. Thus, you can easily use them in calculations and get answers that are either dates or a number of days depending on the calculation.
In your case, datefield1 - datefield2 will return the number of days between the dates stored in the two fields.
Use this expression to get the number of days it took to get a response:
get ( currentdate ) - yourtable :: yourDateField.
If you define this in a calculation field, make it an unstored calculation so that it always recalculates with each new day.
Thanks so much. You went above and beyond answering my question. It turns out that what I really needed to do was as simple as Get (Current Date), but to mark it as "unstored."