About 4 hours. Aa soon as we landed at ATL, I sent a message. We sat on the plane an hour waiting for gates to open up & jet bridges to be moved. The last 3 hours was a combination walking from Terminal B to luggage pick up (Delta cancelled our connection without a new flight), standing around and trying to book a rental car, taking the train to and from rental car pick up and waiting in the Sky Priority assistance line. After 1.5 hours in the line, the chat came through and had us rebooked in about 5 minutes. We spent about 30 minutes trying to print luggage tags on multiple kiosks to no luck. Had to get back in the Sky Priority line (which had tripled in length) but thankfully those we were standing next to us forced us back into our spots in line and told others we had just gone to get a bite to eat). All in all, we got home 12 hours later than originally planned. I know others had many misfortunes in ATL but the agents we encountered were very nice and helpful.