In previous Ryder Cup events held both in the US and Ireland, Tour Rentals has found that many homes were pre-rented in advance by people representing corporate and media clients, months if not a year in advance of the Ryder Cup.  Naturally, they want to secure the accommodation early so they may arrange the myraid of details required to move and service large groups.  Since the cost to list a home is a single, one-time, full duration fee, it is better to be early to maximize the exposure by beginning the marketing phase at the earliest possible date.