Seems fairly straightforward. You search for the text in the file over the appropriate time range (e.g., midnight to 8:30am, run at 8:45am). Then send an alert if the count of results is zero, or less than 1. That is an option available when configuring alerts.
index=WhatYouChoose "OmniKrnlService.main" earliest=-0d@d latest=-0d@d+510m | stats count | eval Flag=if(count>0,1,0) | search Flag=1
This would have you searching between midnight and 8:30am each day, but there isn't a solid way to decimal point it
(510 minutes from midnight is 8:30am)
| search Flag=1 would mean you found results
| search Flag=0 would mean you did not find results
Seems fairly straightforward. You search for the text in the file over the appropriate time range (e.g., midnight to 8:30am, run at 8:45am). Then send an alert if the count of results is zero, or less than 1. That is an option available when configuring alerts.