BTW - I found this documentation about the job schedule:

[ @freq_subday_interval = ] freq_subday_interval

The number of freq_subday_type periods to occur between each execution of a job. freq_subday_intervalis int, with a default of 0. freq_subday_interval is ignored in those cases where freq_subday_type is equal to 1.

So does this mean that when the job has completed that it calculates that interval?