There are a bunch of splunk answers already on this subject. First read the answer here: https://answers.splunk.com/answers/129424/how-to-compare-fields-over-multiple-sourcetypes-without-join-append-or-use-of-subsearches.html#answer-129426
Specificically in your case I would start with something like this:
(sourcetype=changes OR sourcetype=Ticketcenter) | lookup deviceip_devicename deviceip AS <fieldname of ip address in sourcetype=changes> OUTPUT devicename | eval session_time=if(sourcetype=="changes",_time,NULL) | eval ticket_time=if(sourcetype=="Ticketcenter",_time,NULL) | stats values(*) as * by devicename | fields <as desired>
You should be able to validate the times with an additional |where command comparing the two time fields. It can be hard to shake the idea of requiring joins - try to think of Splunk as one big table!
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