We use ES 5.4.
Per Date Histogram article, there does not seem to be an option to request six months histogram.
Available expressions for interval: year (1y), quarter (1q), month (1M), week (1w), day (1d), hour (1h), minute (1m), second (1s)
Also note that time intervals larger than than days do not support arbitrary values but can only be one unit large (e.g. 1y is valid, 2y is not).
Scripting also does not seem to support this since it uses DateFields mentioned on the website
I was wondering if there is a workaround for this. Thanks so much.