I ran into the same problem today and found your post. I was able to work around my issue in the source-code for my web app, where I have my form links embedded.
If you have access to the source-code, you may be able to get around this in a similar fashion.
My app is a Ruby on Rails app, so in the controller for the page I have my links embedded in, I just made an instance variable
@today = DateTime.now which will be available to that view.
Then in the view, I interpolated that variable into the link URL like so:
<a href="...airtable.com/12345?prefill_Date=<%= @today %>"></a>
This worked for me - notice the URL and the pre-filled Date field:
I’m afraid I can’t be of much help for frameworks other than Ruby on Rails, but hopefully this points you in the right direction