Create Outlier Flag Column with Date Range Filter

I have 2 columns: DateSent (Date/Time) and TurnaroundTime (Integer).

I want to create a 3rd column that would flag rows (1 or 0) whos turnaround times are outliers from rows that were sent within the last 30 days from the rows date sent.

i.e flag the row if the turnaround time is > 1 standard deviation of all reports sent within 30 days from this rows DateSent.

I have tried a number of calculate functions with filters, but I just can't seem to get this working.

Any help would be greatly appreciated!