I think you’re getting confused about how to create variables in Bubble. (Local variables are called “Custom States”.) You’re likely also getting confused about the presentation layer versus data layer.
Anyway, here you go:
Runtime: https://list-shifter-demo.bubbleapps.io/version-test/date-incrementer?debug_mode=true
Edit mode: https://bubble.io/page?type=page&name=date-incrementer&id=list-shifter-demo&tab=tabs-2
For more on dates (actually, watch this before you even attempt to inspect the project I posted above) see, Live Bubbling with Keith: Let's Talk About Dates - Explaining the Basics of Dates in Bubble