Buzzr has aired at least two episodes where someone on the team prematurely saw marker #3 and didn't touch the product (one time, they started to lunge for the product, then pulled back when they saw it was #3), so it seems clear that grabbing the money early wasn't allowed.
At one point, David Ruprecht would frequently the bonus round by saying, "Remember, you have to solve the first two clues before you can go for the $5,000."