At GMAT Pill, we'd recommend you take your GMAT soon (perhaps now) before you gain your work experience. It's very difficult to balance taking the exam while doing well at work, all at the same time. Further, you'll have to do a number of things on top of work -- GMAT, networking for recommendations, and time to ponder your application essays.
And remember, your score is valid for 5 years. Read this GMAT Pill [url=No worries, you're not rushing into this. Taking the GMAT earlier is usually better. It's really hard to balance work + studying - especially when work requires strict schedules and studying requires continuous concentrated effort. If you do take the GMAT while you are working, I definitely recommend you take vacation days so you can have that continuous period of concentrated study.
There are many reasons why you should take your GMAT at the time you are trying to (right now). It sounds like you want to apply some time in the next 5 years. This is a great time to take because you can give it a good effort now and you'll be eligible to use your score to apply after 2-4 years of experience and not worry about timing. The average time for bschool applicants is around 3-4 years of work experience. Taking the GMAT now lets you focus on work stuff -- doing well on your job, networking, taking care of emergencies at work, and learning how to get measurable results at work. Developing relationships is key because you'll also want letters of recommendation, etc. And then when you actually do apply, you'll need to spend time with essays. GMAT on top of all that is simply too much.
So you're in good shape. Take it soon. Have a plan -- and save yourself trouble by acing it the first time. No more second chances in order to save yourself time. That's why your thinking process really matters -- not just a lot of practice. We emphasize that with video so do your research on your prep provider.
There's a really good article on the thinking behind taking your GMAT early. Have a look:
https://www.gmatpill.com/when-to-take-th ... ly-better/]article[/url] for more details.
As for top business schools -- it depends on what you mean by "top". Many of the top tier business schools will require a score of at least 650. Certainly the averages for the top scores are over 700, but if you want to even have a shot at the top schools + 2nd tier top schools, a 650 score is a good target at the low end.
Bschool admission is getting very competitive. So keep in mind, a higher GMAT score will always help (try out the GMAT Pill videos -- there are free RC videos on the site, look for them). But you'll also need to balance it with a good professional background that sets you apart from others.