The current behavior of `org-add-planning-info' does not include 
the time of day when
it is passed the TIME argument. This is because 
`org-time-was-given' is initially let-bound to nil
during the scope of the function.

The attached patch removes that binding and allows the caller to 
pass the time of day in the above case.

An example use case I use with org-capture templates:

(defun +org-schedule-relative-to-deadline ()
  "Prompt for optional deadline, then an optional schedule time.
The scheduled default time is the deadline."
  (interactive)
  (condition-case nil
      (org-deadline nil)
    (quit nil))
  (let ((org-overriding-default-time (or (org-get-deadline-time 
  (point))
                                         org-overriding-default-time)))
    ;; works with patch, but without it the time of day is not 
    included in timestamp.
    (org-schedule nil (org-read-date 'with-time 'to-time nil 
    "SCHEDULE: " org-overriding-default-time))))