Epoch time format error

Hi, I am using Grafana 1.7 with Influxdb 1.7 as data source.

Query is below:
SELECT non_negative_difference($__from - $ONDur_First) FROM “EMS-Smart-IOT-Device-test1”
Query Inspector view:

Either I have to covert the “$__from” to unix format or need to convert unix to YYYY-MM-DD…format.
Please suggest a way out.