You can try the same script as above with adding num function in the beginning to convert into num format.
num(alt( date#(date,'MMM DD YYYY'),
'No valid date')) as newDate
if you want to convert everything into particular date format try
date(alt( date#(date,'MMM DD YYYY'),
'No valid date'),'your date format') as newDate
I did Sunny Talwar example's and worked perfectly.
I Attached a app with this example.
I note that have a date "02-29-2017", but how february don't have 29 day the qlik changed to "03-01-2017".
Note i did two diferents data formats.
And i use floor command to convert to number.
date.qvw 153.5 K