A lot of great info starting with this page flydulles.com - Parking Information and timing is estimated in the detailed FAQ: flydulles.com - Parking Frequently Asked Questions

It's a very busy travel weekend but you might get lucky with a drive up open space in a garage (so maybe reserve economy and try your luck with the garages?).

The frequency of Economy Lot shuttles has been increased from 10-15 minutes to 7-10 minutes with about 10-15 minutes of actual travel time - I would build 25 minutes in to your schedule so there are no surprises and low stress.