Customizing org-columns-modify-value-for-display-function to shorten time-stamps in colview

[Mekeor Melire]

Hello,

I'm trying to customize org-columns-modify-value-for-display-function in
order to change how time-stamps are displayed. I tried this kind of
function:

--8<---------------cut here---------------start------------->8---
(lambda (column-title value)
  (pcase column-title
    ((or "SCHEDULED" "TIMESTAMP" "DEADLINE")
      (if value
        (format-time-string "%02m'%d %a %R"
          (org-read-date t t value))
        ""))
    (_ nil)))
--8<---------------cut here---------------end--------------->8---

But it results in empty (nil, I guess) time-stamps being displayed as
the current time; and non-nil time-stamps being displayed with the
current hour and minute. What's wrong?

Kind regards
Mekeor