What Class determines Class Time Spent in Battlefield 3?

Solution 1:

The class timer is ALWAYS determined by the class chosen when spawning. The server takes this data and starts the timer. You create a profile on the server when joining a server, with default class = Assault (that's why you see assault as the first class "already chosen"). You cannot log in to the server unless this profile has data on it. (assault, and all values = 0)

When you see the scoreboard, the server creates that data from each of the player's profile. If you see a little wrench, cross, crosshair or bullets, then you know what is going to be taken into account when adding time to a class.