Office hours are a useful period of time and are usually for a set period of time every day.  This year, office hours are about 15 minutes before band starts and about 15 minutes before school starts.  Office hours are a time for talking directly to Mr. Bender as talking to him during class time can be difficult because of the case of this occurring, Mr. Bender may have the lab open during lunch so that lab materials may be used.  The occurrence of this varies according to the requirements of the projects assigned; however, Mr. Bender will tell you if the lab will be open for use during class. 

Usually, before a test, a review session will be held by Mr. Bender.  Typically an hour or two on the day before the test, this is useful if you don't understand the material and need to go over it again.  A less extreme solution (2 hours after school!) is just to ask a friend who has a history of knowing what's going on and usually gets good grades.  amount of material covered each day gives little extra time to speak with him and the frequency of the labs in the class which means even less time for you to talk to him.  Office hours can be used for things such as clearing up a grading error and requesting information on specific topics (like this O2C).
Sometimes the need arises to use the lab for an O2C or other project.  In Typically, people like these usually are responsible and know the material like the back of their hand (as all chemistry honors students should).  They shouldn't have a problem with explaining the material to you (unless their busy), however habitually asking them to help you can lead to them getting annoyed and becoming reluctant to help you.  In spite of this, asking someone saves on time (usually less than a tutor or after school review) and is good for clearing up a few points you're not sure of.  This may just sound like common sense, which it is, but sometimes people can panic and go to the after school review and get a tutor when they really don't need t.  However, if there are a lot of points you don't understand, go to the after school review, and if you're completely lost, get a tutor.

If you do poorly on KU checks or feel you may get a borderline grade for the semester, join the niner club.  For just 90 minutes of your time, you can get an "A" for your KU checks score and, if you should happen to get an 89, you will get it raised to a 90.  To get into this club, you just need to tell Mr. Bender that you would like to be in it.  Eventually, he will tell you when he needs you to help him with something for 90 minutes (full 90 min in one session).  This usually involves cleaning flasks or doing other misc. tasks.  I'm assuming that this happens after school (if you're in band) although the times vary.