Assuming that your timezone is set to UTC (as the _time shows the date in UTC), try something like this to convert _time to any timezone that you specify in the eval (I'm converting to EST here)
your base search with _time in UTC | eval _time=_time-(strptime(strftime(_time,"%Y-%m-%dT%H:%M:%S.%3N")." EST","%Y-%m-%dT%H:%M:%S.%N%Z")-_time)
It's basically calculating the offset seconds automatically and substracting (or adding based on difference in current TZ versus one that you specify) in in the _time.
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