Something like this should work:
index=ndx sourcetype=srctp srcMsgId=* system=*
| stats min(_time) as early max(_time) as late by srcMsgId system
| where (late-early)>N
Use a value (in seconds) for "N" – like | where (late-early)>90 for a minute and a half, or | where (late-early)>300 for 5 minutes
from User warren – Stack Overflow https://stackoverflow.com/questions/73543582/alert-setting-in-case-of-a-large-interval-between-messages/73546893#73546893
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