<p>I am using the Ajax Control Toolkit Calendar Extender control. In some fields though I want to display the time along with the date. I have tried just setting the Format to "dd/MM/yyyy hh:mm:ss" but the time section gets wiped off. If the user wants to change the time section they can do it manually, the calendar drop down is only used for changing the date part. </p>

<p>Are there any workarounds or alternatives to get this working? </p>

I have a similar issue and I'm planning to use a Date field and an associated time dropdown (in 1/2 hour increments).  User sets the date in the date field, optionally using the calendar control, and pulls down to a valid time.  I plan to have one selection in the time drop down be a "don't care" in case it an "all day" event.
[EDIT] I found this jquery
plugin
that I may end up using.   I also found a link to
Gaia DateTimePicker
in the answers to
this post
(which now looks to be deleted, probably because the OP was asking for WPF controls, not web controls).