Date autocomplete – when to add the separators?

What is a better approach to designing date field inputs?

• Apply the dashes ahead of time (user types 01 and the browser automatically completes it to "01/"
• Apply the dashes if the user types a number when a separator is expected (user types 010 and the browser automatically corrects it to 01/0)

Option 1 seems easier to implement and also seems more straightforward UX-wise. Option 2 is more comprehensive/modern but can easily become a "hidden functionality" that the user is unaware of.

Thanks!