Applescript date conversion

You are close. I think the problem is that you have created two properties (accountName and passwordName) for your text fields but then you are taking the stringValues from those text fields and then trying to store those string values back into themselves.

If you store the values in separate variables the code works successfully.

 -- IBOutlets   
 property theWindow : missing value
 property accountName : missing value
 property passwordName : missing value

 -- IBActions (button clicks)
 on setCredentialsFromUserInput_(sender)
     set uname to accountName's stringValue()
     set pword to passwordName's stringValue()
     display alert "Username is " & uname & "\n\nPassword is " & pword
 end setCredentialsFromUserInput_

The display alert instruction is just there so you can see that something happens when you click OK.

Try:

set dateString to "Tuesday, April 12, 2016 at 12:00:00 AM"
set dateReference to date dateString

tell current application
    -- insert commands here
end tell

Another approach:

set y to 2001
set m to 6
set d to 12
set h to 12
set min to 12
set s to 12

set cd to current date
tell cd
    set its year to y
    set its month to m
    set its day to d
    set its hours to h
    set its minutes to min
    set its seconds to s
end tell