Running org-clone-subtree-with-time-shift and entering an hourly
interval returns an error that the shift specification is invalid.

For example, entering +8h returns:

user-error: Invalid shift specification +8h

I have also tested with just 8 and with .+8h.

The documentation for org-clone-subtree-with-time-shift states that:

> If the entry has a timestamp, the user will also be prompted for a
> time shift, which may be a repeater as used in time stamps, for
> example ‘+3d’.

And the Info page for Repeated Tasks states that:

> You can use yearly, monthly, weekly, daily and hourly repeat cookies
> by using the ‘y’, ‘w’, ‘m’, ‘d’ and ‘h’ letters.

So, as I couldn’t find a reference to this limitation anywhere, I
believe this is a valid bug.

Emacs : GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.23)
of 2020-10-28
Package: Org mode version 9.3 (release_9.3 @ /usr/local/share/emacs/27.1/lisp/org/)

--
Felipe Barros