Hello,
I can help you set the tableau filter date as 'today'. Also, I can provide you with the option to select as 'today,'(by default), custom date range, Last n weeks, month, quarter and year filter option in a single solution (you could just pick any of the option from the drop down as per your requirement).
I'd equally be glad to teach you that how it's done so that you could easily do it for any of your future tableau dashboard on your own.
Look forward to hearing from you,
Sincerely,
Arvind