Do snowballs increase over time? If they don't I guess there's nothing to do in the event for me.
As with all the major events, they increase over time at the same rate as you get Topaz normally. In fact you get the event currency instead of Topaz. It's just that the replacement doesn't actually take effect until you actually start the event by playing while it's active, so you keep getting Topaz until you actually get in the game.