So this Timezone option looks very useful.
https://cwiki.apache.org/confluence/display/solr/Working+with+Dates#WorkingwithDates-TZ
Example,
http://localhost:8983/solr/my_collection/select?q=*:*&facet.range=my_date_field&facet=true&facet.range.start=NOW/MONTH&facet.range.end=NOW/MONTH%2B1MONTH&facet.range.gap=%2B1DAY&TZ=America/Los_Angeles
Note TZ=America/Los_Angeles
But I can't work out how to set this option via the Solarium API.