Response Time After Interview?

On average, how long does it take to hear back from an interview? I interviewed a week ago for a TA position and it went well (I have a full-time job and have only had one other interview in 7 years so I felt… rusty.). The OM told me I’d hear back by Monday, but it’s come and gone. I know they’re super busy, though. If I just need to sit tight, I will!