When you consider your Grand Opening, think of it like a honeymoon.  You are trying to get your customers to know you, so you want your Grand Opening to last as long as possible.  Too often businesses hold their Grand Opening event for only one, two, or three days.  Now sure, you can have a one day "ribbon cutting", but make the "event" last as long as possible.  In the big picture of the life of your business, a two week or month long Grand Opening is not a long time.  This is the "honeymoon" your potential customers need to get to know where you are, and that you are open to service their needs. 

Another trap many owners and managers fall into is the "small mindset" mentality.  Simply put, they have been eating, dreaming, sleeping their new business for so long, that it is the most important thing on their mind, and they think it is the most important thing on everyone elses minds as well.  Well, face it, it is NOT a big deal to the thousands (of potential customers) that pass your new location every day.  A good bet is that MOST of them have no idea you are opening a business.  That is the reason for the GRAND OPENING event.  It is the time to reach as many customers as possible with the news of your business.