Hello, 

Dynamic Default value is Not Support by odoo Studio

If you Want to current Date then we have one more Idea.

You will Create the Fields As Compute

Readonly = False

Stored = True

Dependencies = partner_id

# Please Make Sure in Dependencies it was use every time when you Filling the Data so most probebly use required Fields

Compute

=======

for record in self:

record ['x_studio_date_field_name'] = datetime.datetime.now ()

So in above method when the Customer will change the it will compute and set the Today Date or Datetime.

Thanks