I'll agree with everyone above. Yes, the earlier questions are slightly more important, at the very least because you want to "get the ball rolling" and feel like you're off to a good start. Confidence is a big thing on the GMAT.
At the same time, you certainly don't want to spend over about 3 minutes on any question, even the first few. After about 2 minutes, either you know it or you don't. In other words, at that point you're probably just guessing.
The way I tend to approach earlier questions is that I won't sit there for 3 minutes trying to figure it out; if I don't know it after a couple minutes, I'll guess and move on. However, if I *do* feel like I knew the question, I might take an extra 20-30 seconds to check my work just to be sure I didn't make a silly mistake.
All that said, I like the advice given above: you only have one question at a time on your screen. Worry about that question. Don't try to game the system or overthink the test.
Jim S. | GMAT Instructor | Veritas Prep