This is one of the puzzles I linked a ways back, but deserves a re-link now in this new format:
Game type: Browser-based word puzzle
Time demand: Overall, fairly good, although it does have a save button for coming back later so that you can put in as much as you want at a chunk. (Don't know how well the save feature works though.)
What it is: The puzzle starts off with one phrase, "on the farm," and is surrounded by empty boxes showing only the number of letters needed. Your job is to type words or phrases associated with the farm into the response box, and as you guess correctly, the responses appear on the game screen.
It doesn't stop there for course - as the new responses appear on the screen, they open up new chains leading off that new word. And so on, and so on. There are actually 25 different screens that eventually unlock as you get further and further from the original farm, and it can really wrack your brain to get there. If you like word puzzles though, you should really give it a try.