First, you will need to add a custom date type field in your Bob in order to have a date that will work as the anchor date for the task list.
Next, when setting up the task list, select the custom field as the anchor date, then you will need to count the days from the anchor date that you want the task to be triggered.
For example, let's say you created the task and the anchor event is 01/04 the first task will be set to be triggered 30 days after
The second task will be set to be triggered 60 days after
The third task will be set to be triggered 90 days after
and so on…
(You would need to adjust the numbers as some months have less and more than 30 days)
Please note that you will need to update the anchor date once a year in order for the task to trigger correctly for the next year.