It can vary, depending on the tumor type. Remember that by the time you've been diagnosed, your tumor has been growing for a while, so in most cases, a few weeks, or even months, one way or the other won't make much difference.
My first surgery was the one of surprise discovery. Then I went to Memorial Sloan Kettering, and they did not do their surgery - the follow-up, and clean up, for 4 months. They felt there was no hurry.
Yes, we want this cancer out of our bodies, but in some cases, it is better to delay surgery, and shrink tumors with rads or chemo first. Sometimes, they need to let your body heal from a prior procedure, as inflammation can look like tumor, so residual inflammation can result in more extensive surgery being done than was necessary.
I understand how you feel - wanting this part over and done with. Spend the next few weeks out and enjoying your life, getting as fit as you can before surgery slows you down for a while. I bought a kayak between my surgeries, and spent as much time on the water as I could - good for both mind and body.
There is also a pre-surgery mind-body meditation CD that Sloan Kettering produces - you might want to get your hands on that and practice 20 minutes a day, to help you through the next few weeks. (Contact MSKCC, and you can order from them.)
Take care of yourself. Try to remember to breathe. Somehow, you will get through this - we all do.
Sending strength and hugs,