I know this is 5 years old, but I found this post via Google and used it to configure a custom datepicker successfully on the current version of Grappelli, with one issue, that it didn't work on newly created inlines. Just figured out why so I thought I'd post the solution here - as well as overriding the grappelli.initDateAndTimePicker function you *also* have to override the grappelli.reinitDateTimeFields function, passing in the same options you defined in grappelli.initDateAndTimePicker (for obvious reasons it's probably better to declare the options object outside both functions so you can just use the same options object in each). Hope that helps someone!