[Orgmode] How do I insert just a time stamp in a capture template?

[Charles Cave]

I use capture to log how I am spending my time. Every time I start a new task, 
drink a cup of coffee, have a break, arrive at work, go home, I want to quickly 
capture a note.

I use the following template

("l" "Log Time" 
    entry (file+datetree "c:/charles/My Dropbox/GTD/timelog.org") 
    "** %U - %^{Activity}  :TIME:")
)

A typical entry from this template looks like:

* 2010
** 2010-12-December
*** 2010-12-09 Thursday
**** [2010-12-09 Thu 08:10] - Arrived at the office           :TIME:

I would like to just have the time in the headline not the complete date time
stamp.

I couldn't find a % extension in the documenation
(9.1.3.2 Template expansion)

How can I just include a time only in the heading?

Charles

P.S.  My capture-mode tutorial project should be released this weeekend