In the attachments is a better version with tests that also addresses 
your latest critique.

On 13/08/2023 14.44, Ihor Radchenko wrote:
 > Ihor Radchenko <yantar92@posteo.net> writes:
 >
 >>>               (while (or (= nshift 0)
 >>> -                   (not (time-less-p nil time)))
 >>> +                                   (not (time-less-p nil (time-add 
time-to-extend time))))
 >>
 >> And this compares "now" with year 1970. Will always return nil.
 >
 > Hmm. I somehow missed `time-add'.
 > However, this is still fishy.
 > What if we have something like <2023-08-13 2:00 ++8h>?
 > `org-extend-today-until' should probably be ignored then.