Hi Wylie,
Glad it's not just me confused...! Thanks for the quick follow up too...!
Below is the setting for discover::searchFieldsFromSource
A portion of the expanded document in Kibana that shows elapsedtime as '3' in Kibana, rather than the expected '3.039' is shown below. In the expanded view it also shows in Kibana as '3' so this isn't an artifact of the line-view.
The index pattern for my elapsedtime field is as follows:
and finally the setting for format:number:defaultPattern is:
I'm not sure I see anything obviously wrong with any of these....and this seems to be working fine on records that are prior that timestamp... 
All help appreciated!
Regards,
Steve