This study reports on the direct observations of customers in two U.K. betting offices gambling on horse and dog races. These observations revealed that bets were more frequently placed in the last minutes just prior to the start (the OFF), and that this was caused by high-frequency gamblers (customers who had eight or more bets in a session) consistently placing their bets in the last two minutes prior to the OFF. Low-frequency gamblers (three or fewer bets/session) avoided this time period placing their bets earlier, or after the OFF, i.e., on a later race. It was argued that the betting behavior of the "gamblers" could not be explained either in terms of "skillful betting" or solely in terms of variable ratio schedules but was more adequately accounted for in terms of an interval schedule. It was further suggested that time-based schedules might be of heuristic value in generally understanding persistence at gambling while losing.