Hi there, I gave it a test and it seemed to work fine(ish) on my end. I couldn't manually put it in my document metadata (due to there being a max input) but if it's allowed to do it's thing automatically it put the date in correct. 

Does this example look correct to what you're trying to achieve? I think we might be out of luck for inputting manually as a date field as it doesn't seem to accept the extra characters while typing in. I could be wrong but I think if you're wanting to type the dates in manually you'll have to use another data type, multiple values formatted in this way or two different date fields.