Try like this
your current search with datefield1 and datefield2 which you want to subtract for duration
| eval duration_secs=strptime(datefield2,"%Y-%m-%d %H:%M:%S.%N")-strptime(datefield1,"%Y-%m-%d %H:%M:%S.%N")
| eval duration_str=tostring(duration,"duration")
Hello there,
Assuming you have your timestamps as start_date=2018-03-29 10:54:55.0 end_date=2018-04-29 10:54:55.0
Give this a shot,
your_base search
| eval start=strptime(start_date, "%Y-%m-%d %H:%M:%S.%N")
| eval end=strptime(end_date, "%Y-%m-%d %H:%M:%S.%N")
| eval difference = end - start
| table difference
Additionally, have a look at the below links for more details.
https://docs.splunk.com/Documentation/Splunk/7.1.2/SearchReference/Commontimeformatvariables
https://docs.splunk.com/Documentation/Splunk/7.1.2/SearchReference/Convert
http://docs.splunk.com/Documentation/Splunk/7.1.2/SearchReference/DateandTimeFunctions