I tend to agree with Stacey's comment regarding the initial questions being important.
Here's my take on this: If the first question was of medium level difficulty where the program assumes that everyone is at the same level; a person who answers the first question right will get a question that is more difficult (relative to the first one) and if s/he get's it wrong then the level of difficulty is less (relative to the first question). So going with this reasoning if a test taker spends a big chunk of the testing time on the first few questions (and get's them right), the questions that follow are only going to be harder to answer (according to the claim made by the test administrators). This will leave you with lesser time to complete the section. And as Stacey pointed out if you leave a section incomplete, all the incomplete questions are marked wrong.
Therefore IMHO, its best to allocate equal time to answer each and every question. Its okay to guess if you are unable to get the answer, just make sure that the guess is an intelligent guess. I know its easy to preach but difficult to follow, and here's where practice plays an important role. The more you practice the better you get.
Good luck! I will need lots of it too, come May
Cheers!