Set timepicker available hours

I am trying to restrict the Timepicker hours to the open hours of a store. I put this in:
add_action( ‘wooccm_js_timepicker_additional_args’, ‘custom_wooccm_js_timepicker_additional_args’ );

function custom_wooccm_js_timepicker_additional_args() {
‘minTime’: ‘6:00am’,
‘maxTime’: ‘4:00pm’,
‘showDuration’: true
}
But it isn’t working – the site goes blank. Please help.