Formatting Date And Time As A Single String

Caveats
If you have windows, the only way to do this in a way that will show up in exports is to create a string representation of the date in the elasticube and use that. There are limitations. If these are significant, look at a move to Linux. 
This solution and all solutions besides just creating a string in the elasticube will require scripting. Designers may not understand how to do this. 
If you are on Linux 8.2.1+ the pivot2 api will allow widget scripts to also show up on pdf exports.
This solution is applicable only to pivot tables in Linux 8.2.1+
Step 1
In your model, create a custom field that is seconds from epoch. 
In Sisense you can do this with a custom column like:
Step 2
Use a widget script to format the date time
Results
Before
After
Cheers