[TYPO3] Start/stop fields - date & time instead of date only - how?

[Christoph Luehr]

On 26/04/07, Dmitry Dulepov <9f4eetb02 at sneakemail.com> wrote:
> Christoph Luehr wrote:
> > in wonder if (and how) it is possible to change the
> > start/stop fields of the page properties and content elements
> > in the section "General options:" so that the user is
> > able to enter a time (in addition to a date ..).
> >
> > Any ideas and suggestions would be greatly appreciated.
>
> Probably you need to modify TCA for 'pages' table. That field most
> likely has "eval" property set to "date". Try setting it to "datetime"
> from extension and see if it helps.

Thanks - sounds like the right way to proceed.
But how do i modify an existing field of a table?
I only know how to extend a table - like this

t3lib_div::loadTCA("pages");
t3lib_extMgm::addTCAcolumns("pages",$tempColumns,1);

Thanks for the advice.

Christoph