(apply 'encode-time
	 (parse-time-string
	  (cond ((fboundp #'iso8601-parse) "2020-06-24T17:00:00+0200")
		(t (concat
			 (mapconcat #'identity
				    ;; TODO: Eventually replace hard-coded string
				    ;; index values with something more elegant.
				    (split-string (substring "2020-06-24T17:00:00+0200" 0 19) "T")
				    " ")
			 " +0000"))
		(t "2020-06-24T17:00:00+0200"))))



result:
(24307 27248)