AVG line with 1 STD deviation from historical data in line graph

grafana v7.0.5 — and graphite.

I plotted out run completion time each day (M-F) for a specific task. Using Max value each day for series.

I am trying to create a threshold line with standard deviation that will look back N days worth of data.

Query looks historical 30 days and gets average completion time is 20:00 and 1 std dev is +/- 10min

so line will be across 20:10 and 17:50 filled which will represent normal runtime of this task.

Is this do-able? if yes, how?