Some Eldorado Canyon timed-entry slots are released on the day of the visit itself.
Eldorado Canyon State Park requires a free timed entry reservation, booked through CPWShop.com, for vehicle access on Saturdays, Sundays and summer holidays from May 1 through October 1, per CPW's own park page and local coverage. Most slots open 30 days out; some same-day slots are released. We watch for both and alert when a slot opens.
Updated , checked by hand against the target's own page.
Watched from cpw.state.co.us, the target's own public page — not a reservation system we poll.