Before I get ahead of myself, let me tell you I am an Infantry O candidate with BMOQ and CAP done. I have zero experience in the actual job and most of the following is my "impression," which will vary with how accurate is, but I am sure someone can clarify where I am wrong.
The forces.ca site is down right now, but I believe it says you spend around 67% of your time in garrison and 33% in the field, so that will give you an idea of frequency right there. It may be 4 weeks in the office, 2 weeks in the field, or 2 in the office, 3 in the field, etc. That will always vary of course, but it's an idea.
Now, consider what you will be doing in the office. As Michael has said, they will be important. It's not necessarily staring blankly at black and white and thinking about how bored you are. You will be doing various things that comes down to one thing: looking after your troops.
One thing I have experience with from EWAT is the NPF Audit for a Major at a Cbt Engineer and an Infantry unit. Basically, they get certain funding for certain things, so a Physical Fitness Maintenance Grant of "x" dollars is one of them. This money is pay for equipment or various other things necessay to help troops in the unit maintain physical fitnss. They have to make those decisions, and hey have to properly account for where that money was spent, and how it was spent. Whatever money they don't spend in the year, they lose (in other words, their troops lose... if there's $1000 left in that account on April 1st, that's $1000 that the troops could have benefitted from but won't from their failure to utilize it). That's one account out of between 8 and 12 for each that I was preparing for an audit. As you can see, it's important for them to be on top of this administrative type duties, and you might find that it's not so boring when you can see the direct results (the benefit to the troops) to your good work, or if you can see the potential benefits lost due to your poor work.