As already told, the next notification will be created when you run RISTRA20 (IP30). In your case, the period of scheduling can be 1 month. If the start date is given as 29.06.2015 in SM36, then next Notification will be created on 28/29.07.2015 when the RISTRA20 runs through the background job, (Provided your previous notification is completed before this date- this is because of the Tick). In case the previous Notification is not completed and the RISTRA20 run on 28/29.07.2015 does not create any Notification.
I do not think the initial scheduling through IP10 for 6 months is necessary in this case od background job scheduling. Means even you do not have those 6 lines of schedule Hold in the IP10 screen, your Notifications would get generated every month.