MISSING CUSTOM DATE FACILITY ON IPAD IOS 6.0 CALENDAR APP.

Just upgraded my Ipad 3 to IOS V. 6.0 and noticed that facility to insert a specific custom event date period in Calender not available. Wish to program specific events occurring 4 weekly and not monthly. Repeat periods available from None, Every Day; Every Week; Every 2 Weeks, Every Month and Every Year, however if one wishes to program events to occur every 4 weeks, no longer available. This custom date facility does exist with Ical v. 5.0.3 on my Macbook and Imac. Cannot understand why this facility does not exist. Makes syncing between appliances a waste of time. Am I missing something here? NickGS