I would assume by "hard mode" they meant the last 3 difficulties you unlock by beating the first 3. And the challenge at that point is chasing even higher times

I would assume by "hard mode" they meant the last 3 difficulties you unlock by beating the first 3. And the challenge at that point is chasing even higher times and doing leaderboard chasing (though good luck cracking the top 200 at this point, my 250+ is only 317th last I looked).