Following Up after an Interview

[Heterozygish]

I have interviewed with two PhD programs over the last two weeks. The first one accepts students into the program and then they do rotations, and in the second students must enter a professor's lab right away.

Currently, I haven't followed up on any of my interviews. At the second program, I don't feel that I'm a good fit in the lab I interviewed, so I'm going to send an email to that affect and thank her for her time. 

However, for the first program how important is it to send a follow-up/thank-you email after? I didn't think about it right after because I was prepping for the next group of interviews, and I only need to be accepted by the program and not a POI right off the bat. Is it too late (the first program interviews were 1 1/2 weeks ago)? 

[h-bar]

1.5 weeks seems a little late... The usual advice I've heard is to send the thank you email one or two days after the interview. Depending on department timelines, they might already have moved on to the next phase in considering your application. 

[SocialPsycNerd]

Sending a thank you email is incredibly important, even if you don't feel that you were a good fit. While thank you/follow up notes should be sent between 1-2 days following an interview, it's definitely better late than never.