Every time you throw a snowball, it roll the dice to see if you earn something.  You earn it right there and then, in real time, privately. 

We will not be capping what you earn* (except in cases where it hits max)

(extreme examples below)

If you throw enough snowballs to get 300 wack, then you got 300 wack (since there is no max)

If you get a +1 to your defense 20 times, and that puts you at fully maxed, then your 21st will randomly roll a different stat.