How to set up default value for date field in Maniphest form?

Hi all,

In our installation, we created two custom fields in maniphest:

      "company:task:start-date": {
        "name": "Start Date:",
        "caption": "Please pick up start date?",
        "required": true,
        "search": true,
        "type": "date",
        "default": "today"
      "company:task:due-date": {
        "name": "Due Date Before:",
        "caption": "Please pick up due date?",
        "required": true,
        "search": true,
        "type": "date",
        "default": "tomorrow"

But, default value does not have any effect.

For due-date we also tried combinations, like:

today at 6PM
today + 1 day

When we edit default value while editing form, what should we put for this two fields?
Basically, we would like to force start date field to “Today at 8AM”, and due date field to “Tomorrow at 6PM” during task creation. Any suggestion how to do this?