This system is usually run by the estate sale company and numbers are given out starting at a particular time prior to the opening of the sale. This does mean that at times there will be a First Come First Served line just to get a number to enter the sale. Most companies give out numbers at least an hour or several hours before the sale starts. This gives people time to go do more hunting or eat breakfast before the sale opens. They do not have to wait in line for the sale to open. Usually your number is good as long as you are in line when the sale opens. If you are not in line and your number is passed then you must go to the end of the line and your number is no longer valid. You should know the policy of the company holding the sale.