That's 677 total puzzles. But remember, it says that there are in total 11 areas, of which you need to complete 7 or 8. And it says that to complete an area, you don't necessarily need to solve every puzzle within it.

So let's say you need to solve, on average, 75% of the puzzles in an are to beat it. And that you need to solve 7 out of the 11 areas. That gives you (677 * 7/11) *.75 / 40 or about 8 puzzles per hour.