The official beginning of a new business is different for everybody. I would caution that getting caught up in the administrative setup of a business -- including finding office space and fitting out that space -- is an extreme distraction to actually doing business.
Many first-time owners get caught up in those activities thinking they are doing actual business when nothing could be further from the truth. So while you're getting your paperwork completed, you also need to be engaged in the "business" of your business.
It's important to ask yourself these question:
Do you have a targeted prospects/suspects/customer list or database setup?
Do you have a good base of suppliers or vendors you can rely on?
Do you have all the numbers of your business worked out? Do they add up to cashflow and profit? If not immediately, when? Is there something you can do now to help shorten that gap?
Do you have systems to generated qualified leads? Do you have a strategy for generating repeat business (knowing you probably won't be profitable on a per customer basis until the third or fourth purchase)?
Planning and getting things in place for items like these will not only make you feel like you are doing more official business, it will actually help you in and on your business.
Congratulations on taking the first steps to ownership, and if anything, you'll realize the definitions of your business and your success will largely be defined and driven by you.
So if your LLC application date works for you, you've just notched your first milestone in what will hopefully be a long and successful entrepreneurial career.