(defun my/org-refile-to-journal ()
  "Refile an entry to journal file's date-tree. Journal file needs to be an agenda file."
  (interactive)
  (require 'org-datetree)
  (let ((journal (expand-file-name "journal.org" org-directory))
        post-date)
    (setq post-date (or (org-entry-get (point) "TIMESTAMP_IA")
                        (org-entry-get (point) "TIMESTAMP")))
    (setq post-date (nthcdr 3 (parse-time-string post-date)))
    (setq post-date (list (cadr post-date)
                          (car post-date)
                          (caddr post-date)))
    (org-cut-subtree)
    (with-current-buffer (or (find-buffer-visiting journal)
                             (find-file-noselect journal))
      (save-excursion
        (org-datetree-file-entry-under (current-kill 0) post-date)
        (bookmark-set "org-refile-last-stored")))
    (message "Refiled to %s" journal)))

(org-map-entries 'my/org-refile-to-journal)