I copied your link and it went to the successful completion page, no puzzle or clue information.
I have only found one or two puzzles that I felt the need to guess as the clues weren't leading me to the correct solution, but feel that I probably just missed something along the way. Occassionally, you have to use deductive reasoning (the same person in two clues using the same day or other criteria indicates that person is or is not that criteria!)
An option you can try is to print the screen with the grid and clues, log out and work it on paper. Your time will still be low, but sometimes it helps to walk away and work it out on paper. Another option is to not start puzzles with the lowest success rate %, just keep clicking NEW GAME until you find statistics you feel comfortable with.
I hope this helps you. Remember that the more puzzles you do, the better you get!