Creating a "hidden" feature for faceted search

[draftvader]

Our offering has a lot of technical specifications one of which is "Drying time" which is represented in seconds.  At present each product has its own drying time, for example "10 seconds" or "14-16 seconds".  This makes this data useless for the filters.  However this data needs to be presented like this to allow customers to see the accurate information.

We would like to either be able to create a second attribute for "Drying time" that groups these together:

< 10 seconds
10-12 seconds
13-15 seconds
16-20 seconds
21+ seconds

This will allow the filters to be selectable checkboxes allowing relative comparisons.  Naturally, however, we would not want this data to appear in the attributes displayed with the product.

The other option is being able to assign a "unit value" to a feature (for example "seconds") allowing us to make the value a numeric digit that would allow us to use a slider filter similar to that for price.

Looking forward to plenty of other suggestions as to different logic to achieve this.
 

Edited July 22, 2020 by draftvader
Mixed nomenclature (feature/attribute) (see edit history)