URL on page to open specific form where date field = today

But no problem.

Just make a helper table with one record in it and the table will only have one field on that one record. Make your URL formula on that field and then make a one record report showing that field. Then put that on the dashboard. If you squeeze in the The dashboard element in between or beside to other elements then you will squeeze the report narrow so it doesn't look funny. It is also possible that you could put the report on the side bar.

So the effect of this is you really have a report on your dashboard which has the button you want but you are trying to make it look as much as a plain old button as you can.