Conditional calculated time column

I’m trying to develop an interview application. These interviews start, say, every Wednesday at 6:30 p.m. and last for 10 minutes. However, there could be 1-3 interviewees on a given week. I envision the start time and number of interviewees as a couple of variables/settings. Then, when an appointment is scheduled (added), if there were two interviewees, I would input 6:30 into the date column for the first two interviews and then 6:40 for the 3rd & 4th interviews, etc. I’m struggling with where/how to do this calculation?

So what you want to do is a form where you can add multiple rows for consecutive interviews?