If you cannot make those hours, then ask your professor for an appointment. Professors at Dartmouth are extremely accessible to students - and you are strongly encouraged to approach them if you are experiencing difficulties in a class. A word about communication. Chances are, you are about to become addicted to BlitzMail. It is fast and extraordinarily convenient.
Many professors rely on it as much as students do.
At the same time, BlitzMail is not always appropriate. Certain kinds of communication are better carried out face to face. Remember that, in college, a crucial part of your education takes place via interactions with faculty outside of the classroom. Often, conversations begun by students seeking help blossom into rewarding mentoring relationships and friendships that are some of the most rewarding educational experiences undergraduates have at Dartmouth. While it may be true that students more often receive a letter from a dean when something is wrong rather than when things are going well, such letters are usually an opportunity to rectify a problem by exploring sources of help or repairing a bruised relationship to the community.