Date histogram on time component only?

I dont know if I'm going about this the wrong way , but I'd like to create a date histogram based on the time component of a dat/timestamp field only ... so that I can "split lines" on the date component , effectively overlaying each days data on top of each other.

I have a timestamp field (date+time) and I can create a date only field, making the splitting lines easy - but if I create a time only field , ES analyses it as a string (and I cant figure out how to specify a time only field type/analyser) .

Also , ideally I'd prefer to use the existing timestamp field and not need to add separate date and time fields.

I believe this used to be easy with groovy scripts , but this is not available anymore? Even so - would the date histogram allow a time only ?
Maybe there is a completely different approach to achieving this ?


One Klunky approach would be to have seperate Date queries.. but thats a lot of work for a rolling scenario. The ES Date types cover Time formats too ( so would it be possible to have an extra time field in your mapping, and then allow Kibana to use that?