ITSO members receive priority over non-members up until 8pm on a Monday evening when a new apartment week is listed. A non-member is able to reserve an apartment week before 8pm but if a member reserves the same apartment and offers the asking price up to 8pm then the ITSO member will secure the reservation (subject to a mandatory 14 day cooling off period).  TIMES QUOTED ARE UK. 

26th September: The International Board met today and reviewed the advantage given to ITSO members, as detailed above. To ensure fairness to all ITSO members for weeks listed as NEW this has changed so that this advantage can only be used ONCE by each member in a 12 MONTH period. The maximum number of weeks that can be purchased under this privilege is 2 consecutive weeks.  This will apply from the introduction of the privilege (May 2022). So, if you have already benefitted from this privilege you will have to wait 12 months until you can exercise it again.  There is no limit to the number of weeks you can purchase after the 'privilege hour'.  We are seeking to give all ITSO members a better chance to buy NEW listed weeks.