At first I thought it was a bug that the challenges appeared only today, it's a shame the system haven't counted all the times we cleared the levels yesterday...
Man it was right who said that they are increasing the milestones with every new event that comes out, that's not nice. One can't pass entire days on this game to get some rewards, the goals should be more reasonable to reach imo.
Anyway I'm not going to even try those 3/4/500 and higher thresholds as the rewards are cheap btw.