I am looking for a 4:30 reservation at Tusker House on March 9th. I entered 4 and 4:30 (in the reservation finder) on two different attempts, but because the search is for an hour on either side of the request, the times that were found were not exactly what we were looking for. When I put in a third request, it said " User has already been taken." What does this mean? Did I do something wrong?