Doing an extra rex on the date field to split out the date parts should work. I tested it using the following SPL and it appeared to work. | makeresults
| eval Message="The previous system shutdown at 10:48:10 AM on 6/11/2020 was unexpected."
| rex field=Message "(?i)at\s(?P<shutdown_time>[^\s].+)\son\s(?P<shutdown_date>[^\s]+)"
| rex field=shutdown_date "(?<month>\d{1,2})\/.(?<day>\d{1,2})\/.(?<year>\d{4}).*"
| eval shutdownAt=month + "/" + day + "/" + year +" "+shutdown_time
| eval shutdownepoch=strptime(shutdownAt,"%m/%d/%Y %I:%M:%S %p")
| table Message, shutdown_time, shutdown_date, shutdownAt, shutdownepoch, month, day, year
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