MySQL Queries to get only runtime/duration, not fetched results
(I have too many Comments for Comments...)


Please provide SHOW CREATE TABLE.  There are many details left out of the Question.
Please provide EXPLAIN SELECT ....  We need to discuss whether it is really doing any pruning.
How many rows are returned by those queries?
Are they realistic queries -- do you really need all columns; do you really need all rows (versus need to summarize them)?
Depending on the indexes, you may find that partitioning is slowing down the operation, not speeding it up.
Let's see the real queries.
The following avoids computing the end date, leap-years, etc.  And it grabs the missing second.


.

      event_time &gt;= '2018-01-01'
  AND event_time  &lt; '2018-01-01' + INTERVAL 2 MONTH


In my experience,


The only purpose for PARTITION BY RANGE(event_time) is to purge old data.
Summary tables are the real 'fix' for performance problems in log tables.


Once you have addressed most of my comments, the title Question should be moot.