That definitely would not work. There are too many random reasons why there might be a small gap in reservations. What about the person that reserved 5 minutes and 1 second after the previous one? Oops, sorry, just missed it. Guess you weren't waiting in line.
Sure it would, it wouldn't be perfect but no other solution would be either. If they wanted to they could look at each store and see that reservations were placed every X number of seconds. Then pick a time period greater than that, I just made up 5 minutes, and say if someone placed a reservation more than X minutes after the previous one, it is very likely they didn't have to wait in line. And neither did anyone after that.
But, I agree with everyone else, this is a silly thing to be debating...