The Front-end / BOD variant would be the cleanest solution, i agree with you. We should add the name of the timeFilter Attribute in the LayersConfig. Then we could specify the Name of this Attribute in the bod.
This variant requires the following adjustments (please complete)
* bod.re3.layers_js new column time_sphinx_filter
* bod.re3.view_layers_js add attribute
* chsdi3 LayersConfig Services etc. add parameter
* this script use LayersConfig instead of test query on index

*pro:*
we can define per layer an individual name of the time filter / time interval attribute 
we dont have to make a test query on sphinx

*contra:*
we have to introduce and maintain a new layer parameter in the bod and in the chsdi services which is only  important for very few layers. 
We are creating a sphinx config cache in the bod

do you see other pros/contras?
I'm not sure yet if its worth the effort to use the bod/layersconfig to get this information.