It was a fast and enjoyable process. After my initial debrief with a very friendly HR rep about my experiences, why I was interested in Target, etc, she set me up with a ~30 minute phone call with one of the technical leads, who was also very friendly. That phone interview was similar to my conversation with the HR rep, but just more technical. She wasn't drilling tech questions at me, she would ask a question like what was your most challenging project, and as I was explaining it she would ask questions like why did you do this.
After that phone interview I was offered an onsite interview, which was fun because they paid for my flight and hotel to come stay out in Minneapolis. I had to do a coding challenge the night before my interview, which was a pretty big coding challenge for the time allotted, and personally I thought I bombed it, but it's all about showing them how you code, how you think, etc. So the next day me and 10 or 15 other kids showed up for our TLP interviews. I met some cool kids, and we had a fun day. You get two short interviews with tech leads and it's more of technical discussion questions, so overall easy. Then you spend the rest of the day eating and talking with engineers to see if you like the program.