Hey there! Totally okay to ask follow-ups – I basically view job hunting as one massive exercise in paying it forward, so if my advice is useful at all, I’m happy to give it.
I think even if there’s only one interview (lucky you!), and you are likely to hear back the next day, it’s worth sending an email shortly after you leave the interview just letting the interviewer know that you appreciated their time and their consideration. Another potential opportunity in this email is to reiterate why you’re the best candidate for this job, ie: “Thanks so much again for your time today; I enjoyed speaking with you enormously and am extremely excited about the opportunity with your institutions. I believe my extensive experience with x, y, and z would help me to excel in the position, and I look forward to speaking with you again soon. Please let me know if you have any follow-up questions, or if I can provide any further information. Many thanks, YOU.”
It’s one more good opportunity to make them remember why you’re the best person for the gig, and you should take it for sure!