Desktop: initial value expression not working. Works on mobile.

[Michuli]

IGNORE POST. MY BAD.

I have 2 DateTime fields. [start date] and [end date].

For the [end date] I have an initial value expression that takes the value of [start date] and adds 1 hour to it. 

It works perfectly on the editor with the mobile preview, but wont work on the desktop web version at all.

Any ideas?