Display events when current date is >= 30 days from expiration date

Spent all day trying to figure this out. The events I'm working with contain a field with an expiration date in Unix epoch time. I'm trying to bring up a table of events when current date is >= 30days before the expiration date. Combed through documentation and Splunk Answers no luck. Thanks in advance. Example data: expiration_date=1548910800000