Well I'm no expert, but in my opinion there are very few, and by few I really mean less than 5% of the problems that truly require more than a minute to solve..
Now if you break down the quants section, you know that you have just a little over a couple of minutes for each of the 37 questions..When I was preparing for GMAT, I used to try to solve a problem in a minute. If it was a difficult question, at least at the end of that minute I would know if I was on the correct track. If I felt I was going wrong somewhere and I was not able to spot the error, I would simply stop thinking about the problem for about 30 seconds. I used to just hum a song I liked in my mind, disconnect myself completely from the problem at hand and after about 30 seconds, read the problem once again and start the problem from scratch...If I was still not able to solve it in the second attempt in a minute, I would guess the answer and move on without thinking if I had got that one right or not..
This worked for me because I realized that I would end up taking about 3-3.5 minutes for solving such problems, but the extra minute or so used here could be easily covered up in other problems which were solved in well under a couple of mins..
Also, I am not sure whether this is true in your case, but try to keep a target GMAT score in mind but don't stress yourself over it. If your target school accepts people at 700, they will accept you at 680, no big deal...In the grand scheme of things, the GMAT is almost always a checkbox rather than a make or break factor..I have found many people stressing over their GMAT way too much which in fact makes them commit silly mistakes rather than helping them...