A lot of readers wonder how much time they should allocate for the naturalization interview and how does the process work. Basically they call a bunch of applicants at various slots because there are several officers interviewing at the same time, a lot of people do not show up, plus they don't really care about your time (and would rather maximize the more valuable time of the officers). In other words, if your appointment is at 10AM it does not mean like a business appointment an officer will be waiting for you at the precise time (it is more like the doctor's appointment which rarely happens on time). Like the whole immigration process, there is a lot of waiting. However, as you can imagine, if a dozen people are called at 10AM someone will go first, so some people might be taken right on time (it is not unusual if you can even be asked to go in early because they are running fast on the previous slot) while others might be taken towards the end (or even later, because like a hospital, officers are some times running late because some interviews lasted longer than others). In other words, simply bring a print book to read because there could be a lot of waiting.
Just know that in addition to going through security to enter the building (for which you should go earlier than your scheduled time), you will wait for your name to be called in. You may either have the interview or the language/civics test first. Let me put it this way. If you are fluent in English, have studied the test that you will answer all the questions correctly and quickly, the language/civics test will last just a few minutes. Lots of waiting, though. The citizenship interview can last a lot longer if your case is complicated or something shows up in your background that requires probing. However, for a resident who has done everything by the book (always in status, no crimes, always paid taxes on time, no violations of any laws ever, no long trips lasting months, etc.), the background is perfectly clean, speaks good English, the interview may not last longer than a few minutes.