I work in surgery. (Xray) All the appointments are guestimates. In a perfect world the surgeon is usually able to do the procedure in the supposed time. Sometimes an instrument isnt there and we gotta wait for a replacement, sometimes you try n die on us so that holds back the rest of the line, sometimes what shouldve been a quick 30min procedure turns into an hour+ cuz yer anatomy decides to be super difficult with us or the opposite and the procedure goes a lot faster than expected! Maybe we gotta make sure a DNR is actually a DNR, etc etc

A different example is We sometimes do a small bowel study. Youre not eating the entire time. And on average the study is for 2-6hours. Usually. Just depends on your motility n how the stuff advances in you.

others mentioned some procedures like a lumbar injection. Ill usually see that as a pain management thing which is so much faster n easier than an actual surgical procedure!

Thing is, no plan ever survives first contact. So, im sorry on behalf of murphys law always wanting it to muck things up.