Hey @team5.amaze!
Thanks for your question.
Currently, default dates suggested in regards to your location.
I think you’re asking for default/predefined values. It’s pretty popular feature request. Unfortunately, it’s not directly supported in Contentful 
But, general concept of workaround could be found here: Creating a default value to predefine checkbox items.
Also, yes, I think it’s possible to tackle it with UI extensions. Have you already tried it? Do you need some help with this?