app/inputs/datetime_picker_input.rb
class DatetimePickerInput < SimpleForm::Inputs::StringInput
def initialize(*)
super
# Format value as iso8601 for javascript new Date() compatibility
if object && (value = object.send(attribute_name))
input_html_options[:value] = value.iso8601
end
input_html_options[:placeholder] = 'MM/DD/YYYY'
end
end