Postbaccalaureate Student applicants have rated the interview process at NIH with 1 out of 5 (where 5 is the highest level of difficulty) and assessed their interview experience as 100% positive. To compare, the company-average is 79.1% positive. This is according to Glassdoor user ratings.
Here are the most commonly searched roles for interview reports -
Submitted application, emailed labs I was interested in and heard back from one I liked. Had a Super Casual Meeting with the PI and was hired the next day. I don't think its worth worrying about as being hired as a IRTA POSTBACC is generally super chill.