Create a custom game with the timer set to 8 minutes and 1 round. This should be more than enough time to find twenty 3-letter words. If you are struggling, make sure you are playing a Word Hunt game (I'm not sure how to scroll the list though and the longest words show up on top so it may not be very helpful) with Portal Cubes turned On. If you are having trouble making twenty words, try connecting three random letters together. You may be surprised to see how many words you didn't know were valid in Boggle. During my try I was able to get twenty-three words. Only 10 - 12 of those words I was familiar with or thought of on my own.