I understand what you are trying to do, but I'm not sure it is possible.
You can't combine 2 basesearch, but in your current setup, you could make a macro for for the "second_base_search"
first your basesearch: Base searches should be a post process search, that returns values you can use all other searches. So you need to include your fruit field, but also your _time
Also you need to secify a timerange for your basesearch, in your case is over 3 months (what you need to split in your second search
It probaly looks somefing lite this:
<query>index=Auto log!=null location=farm fruit=* | rename growTime as Duration | stats perc50(totalTimes) as s50, perc90(totalTimes) as s90 by Duration fruit _time| table Duration, s50, s90 fruit _time</query>
<earliest>$earliest$</earliest>
<latest>$latest$</latest>
<refresh>1m</refresh>
<refreshType>delay</refreshType>
Second part is somethin like:
<query>| search fruit=apple *** some search you get only the correct timespan" | untable Duration, percentile, value | chart first(value) over Duration by percentile</query>
</search>
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