Some confusion from the commenters here mixing up their Group board with the Top 100 board. Today's contest, Klondike Adventure, has JoanPesh and PaltryAmoeba564 at the top of the top 100 with times of 16 and 20 minutes. On my local group board, the current leader took 40 minutes. I finished in 61 minutes. That put me in 7th place, but on the group list, not the Top 100 list.
Can I believe someone else is good enough to do all 20 challenges in 40 minutes without cheating? Yes. But 16 minutes? No. If I used two accounts...the first to determine how to win each game and the second to just click through the answers I already had determined from the first play...I would still have a very hard time finishing in less than 30 minutes.
That said, it's hard to believe anyone is going through that much trouble day after day to play the game, record the best moves, then play a second time. More likely they are using bots or some other automatic way of cheating. Of course, if all you want is to make the top 3 for your group board, then you don't need to cheat as much. Play once, figure out the more difficult games, then play a second time and win within your group. Making the top 100 nationally is going to take more work...or better bots.