I say this with some frequency on these boards, but you really can't compare the environmental exam to others with 80 questions. It's roughly half qualitative questions, which can either help or hurt you. I know people who have worked in only one disciple covered on the exam frequently struggle with qualitative questions.
In my case, I was stronger on the qualitative questions because I work broadly in the field of environmental compliance, and I either knew the answers, was familiar with the topic and just needed to verify the answer, or I was familiar enough with my references to know which 2-3 might cover that topic. I don't think I spent more than 1-2 minutes on each qualitative question, generally, but there were a few I had to spend several extra minutes on.
That said, I finished each half with at least 45 minutes to go. I spent about a half hour attempting quantitative problems that I got stuck on during the first pass through (roughly 5 on each half?), and I had 15 minutes at the end of each to make sure my bubbles were filled in properly. I didn't feel rushed.
If you haven't yet, read through the Consolidated Advice thread on the Enviro board. There's some great info there.
Also, I think you sound like you're studying pretty decently already, so I'd be careful not to burn out. I know personally I wouldn't have used my time wisely during that week in March you're talking about taking off. I didn't feel under pressure until 2-3 weeks before the exam and I really cranked up my studying then. If you're more disciplined than I am and won't end up watching March Madness or Law & Order, then it could be useful. I took Thursday and Friday off before my exam and I crammed on Thursday, taking half a practice exam on my weaker topics and doing a little last-minute refresher on some of the topics I had reviewed early on. Then on Friday I packed my references into my suitcase, got my Ziploc bag of supplies in order (NY has silly requirements), and tried to relax.