The whole process for me only took about two and a half weeks. I was very impressed with how quickly Delta moved.
I applied on Wed, Jan 14, 2015. I received an invitation for a video interview a few days later and the same email the next day. Later that day, I was emailed by HireVue, the company through which you do the online interview with information on how to proceed. I had three days to complete the online interview. I completed the video interview two days later. The next day, around 6 pm, I received an email advising me I would be hearing from a Delta rep via phone call within the next 10 days from 9 am to 9 pm. I was called the following day around late in the afternoon. The phone interview was very quick, about 15 minutes, just a couple questions about tattoos, uniform compliance, and my passport. At the end of the phone call, I was invited to the F2F in Atlanta. It took about three days for me to receive the email with my options for dates. I selected my date (later in that same week).
The F2F is exactly how it has been described. Three rounds, three groups (A, B, and C). Fireside Chat, Destination Delta, and 2-on-1 interview. Expect situational questions during your 2-on-1, utilize the STAR method, and smile. I wasn't smiling literally every second I was there, but I did smile often. Be yourself. Don't interrupt FAs, interviewers, or other hopefuls. Do your best to connect with your interviews, find something that you have in common with them, it makes it much easier to have a conversation with them. Be polite, professional, courteous, and do your best to relax. I know its hard, but its really important not to come across as too nervous or too confident. Remember they invited you for a reason, remind them of why.