A tip for new players: Don't be me. Don't invest anything into crit until you have 5k+ damage and get 500+ skillpoints every level. It really isn't worth anything early on.
I really like this game, but I think that the time attack challenges are way too long. 300 entire seconds of clicking takes away the entire point of this being an "idle" game, especially when the grind is so high that there is no real "active" playstyle. I would love it to be 1-2 minutes, both challenges if possible. The last 3 of these 5 minutes are mostly unused anyways because it takes about 2 minutes to get to the levels you can't beat anymore - so you'll get 5-10 levels maximum in the last 3 minutes of time attack.
 "Sort the Court!"){kind=icon}
 "Endless Training"){kind=icon}
 "Idle Sword 2"){kind=icon}
 "Goldcraft"){kind=icon}
 "Boss Must DIE!!"){kind=icon}
 "Realm Grinder"){kind=icon}