Can I make a form demand EITHER field be required?

Hullo:

I am using a form to track outside vendor shipments.

Sometimes our shipping team gets stuff into the system in advance, sometimes after it's been picked up.

I would like a form that requires either Estimated Ship or Actual Ship. If one is filled, the other doesn't need to be, but at least *one* of them must be filled. (There is an automated workflow in place to remind for actual ships to be filled in later on if they use estimated at the top.)

Is there a logic or dependency option on forms to make that work?