There is a balance to this. Everything you said is correct, but if you feel you have to choose one over the other, a lot of times you need to step back and take another look at the situation. From what I have seen, there will usually be an option that was missed. People will either see the martial arts as a hobby or a path of life. Depending on which one you hold, your approach to your training will be different.
As for the OP's situation, if I was in his shoes, I would have took a look at my personal conditioning and had a realistic check on where I am at, I would have talked to my instructor about the situation and worked with him/her to make sure I was ready for the test, setting up a time table with a scheduled training regiment to get me ready. I then would have checked my job to see what options I had available such as vacation or sick leave incase I needed it for the recovery time and then I would have talked to my manager about setting up my schedule so I can do what I need to do to be ready for the test and minimize the effect it would have on my job.
If you have either an instructor or a boss who is unwilling to work with you with this sort of stuff to make the situation the best it can be, then it is time to replace the one who is not willing to work with you.