A CDO is "last out, first back" flying. Fly the last flight out from the hub and first flight back while remaining on duty all night. You get about 5-7 hours at night at the hotel to rest but the entire day as well. You show at about 8:30pm and usually finish by about 8am, depending on the city and day of the week. Our CDO lines have about 3 of them in a row. Some guys just hang out at the crew room all day between them eliminating the need for a crash pad. 100% commutable since you'd don't need to arrive til late on first day of sequence and can leave very early on last day.

Edit: expect 12-13 days off.