I would recommend you do this in the script and not in the object, but you can use the following code to standardize your dates either in the script or as a calculated dimension.
=alt(date(Date,'MM/DD/YYYY'),date(floor(timestamp#(Date,'MM/DD/YYYY hh:mm:ss tt')),'MM/DD/YYYY'))
It's so complicated because some of your dates are strings and others are numbers. Try to make the dates the same format in the source Excel file.
The rest of the graph is complicated for that reason, so I've attached the QV.
qw.qvw 191.2 K