I was thinking of something like this (haven’t tried yet):
https://stackoverflow.com/questions/4631928/convert-utc-epoch-to-local-date-with-javascript
My JS code/solution would be reusable across items (if I need to track multipe phones or other timestamps in the future). If I can create a oneliner, than the items file would be the only place to define something. With rules I would need to create a rule for each item. (Yes, I know, perhaps lambda’s would work). I like to have DRY code. 
Tried that. Item returns NULL in the log if I do. 