I am trying to customize the graph visualization in Neo4j Browser and I've seen some information on *.grass files to do so. Is it possible to use a grass file to adjust the thickness of the edges based on the relationship duration (e.g., duration.between(Start Date, End Date))? Also, adjust the color intensity based on the same value?
Unfortunately at the moment not, you can only adjust colours and thicknesses based on relationship type.
You could have a look at neovis perhaps for some of your needs.
Or kineviz, yWorks, graphlytics here: