Looks like a similar issue was addressed earlier here:

http://sachachua.com/blog/2015/02/org-mode-reusing-date-file-datetree-prompt/

Shankar

On Wed, Nov 4, 2015 at 2:54 PM, Shankar Rao <shankar.rao@gmail.com> wrote:

> Earlier in org-capture-fill-template, there is the following:
>
> (let* (...
>        (ct (org-capture-get :default-time))
>        ...
>
> The property :default-time defaults to the current time and is overwritten
> by file+datetree+prompt,
>
> If ct was passed as a 2nd argument to format-time-string in your code
> snippet:
>
>       ;; The current time
>       (goto-char (point-min))
>       (while (re-search-forward "%<\\([^>\n]+\\)>" nil t)
>         (replace-match (format-time-string (match-string 1) ct) t t))
>
> this should provide the behavior I'm looking for with
> file+datetree+prompt, but still use the current time for other capture
> types. Will this solution break anything?
>
> Shankar
>
> On Wed, Nov 4, 2015 at 2:15 PM, Nick Dokos <ndokos@gmail.com> wrote:
>
>> Shankar Rao <shankar.rao@gmail.com> writes:
>>
>> > For the following org capture template:
>> >
>> > (setq org-capture-templates
>> >       '(("d" "Date Tree Test" plain
>> > (file+datetree+prompt "~/org/testdt.org")
>> > "This date should be the date i picked: %<%y%m%d>")))
>> >
>> > Though this is filed under the correct date in the datetree, no matter
>> what date I select in the prompt,
>> > the date displayed in the template is the current date. Is this a bug
>> or a feature?
>> >
>>
>> It's a feature I guess - org-capture.el says:
>>
>>       ;; The current time
>>       (goto-char (point-min))
>>       (while (re-search-forward "%<\\([^>\n]+\\)>" nil t)
>>         (replace-match (format-time-string (match-string 1)) t t))
>>
>> and there is no provision for another time to be given here. I don't
>> think there is any provision in the template for a time other than the
>> current time: at least I can't see a %-escape that takes a different
>> time.
>>
>> --
>> Nick
>>
>>
>>
>