Yes i use the access over the mounted network drive over windows.
As long as you see directories items, things, rules and others next to html then you are in the right
That was a good hint because the path then for me is: \192.168.178.232\openHAB-conf\html
I just copied the “lametric.json” file with the content which i mentioned above to this folder and…
Yes it works. Now i’m able to push custom content to the Lametric Time. 
Thanks to the forum and the help from you all!
Now i’ll have to dive in how to modify the file periodically with a rule. Hope i’ll will understand your rule in the near future 