I had some informatic problems during round 1 so I could try only the easier puzzles, which were very pleasant to solve. I think 50' was a good timing for this round.

Then I tried round 2 but did mistake on mistake and so I decided to stop playing and relax. :bleh:

I came back on the puzzles later, and my impression is that puzzles were globally hard, and some really tough. It would have been great to have the round last about one hour and a half.

Finally, the 20' break between the two rounds didn't bother me.

I would be a bit careful about relying on scanraid ratings for human solving. It doesn't seem to correspond too well with actual testing. For example, see Nick Baxter's remarks about the USSC puzzles here (and from direct experience, the 3rd puzzle of the third round was pretty much the toughest one of the bunch).

I agree with this, Scanraid's ratings are sometimes far away from what we could expect. Of course every software will sometimes deliver "strange" scores according to us, but Sudoku Explainer is generally considered more reliable. Anyway I didn't try the tough puzzles yet, so I can't tell about my own experience...