For you to may be...or it may not be. It is a little like asking how long is a piece of string. These guidelines are meant as a basic skeleton to follow. Most people should AT LEAST be brushing twice a day. Some need more based on their diet and oral bacterial environment. Most of us eat several times a day so no, twice a day may not be enough for the guy getting 8 meals down and over 5,000cals.
I keep a toothbrush with me...but then, how would I look in my profession with a dirty mouth?