Tables :: Calculate And Store Time From Dates?

We are collecting data from client files that have multiple dates (start_date, event1_date, event2_date, end_date.) For client protection purposes, we are absolutely not allowed to leave the facility with the actual dates. However, we want to know how many days have passed between each event. I thought about having the data collectors enter each date, have a calculated field store the time between dates, and then have the actual dates cleared when the record is saved or when the person moves to the next record.