I think this should / could work.
You don't need to format your dates using date() functions inside the interval() function, but you need to take care that both dates have a numeric representation (i.e. are QV dates). If you need to interpret strings as dates, use the date#() function instead.
Your single bar, what is its axis label? And what is the value range of your Tran_date and Film_OpeningDate fields?
(I assume both fields are located in one table, right?)