Date custom field types

There appears to be some strange behaviour with your date type.

For example, “stage_change_time” outputs including the time e.g. 2019-06-18 13:24:20
But if I create a date field and try to update it, I may only add a date and not time.

Are your date fields internally Y-m-d H:i:s?

Which date field are you trying to update? Depending on where/type, you are correct, you can update the specific time, but rather just the date.