My situation is exactly like milhouse's ... still not working :-(

Here's what I had to enable proxy objects (using b49)

In Quicksilver Preferences:
1. Under Settings > Application, check Enable Advanced Features; you will be prompted to relaunch when you change this. Once this is enabled, Extras will appear in the left pane.

2. Under Extras, set the Application feature level to Advanced; a manual relaunch is required. Then Proxy Objects will appear in your catalog. (Some other site said to set this to Beta, but, on my machine at least, doing so disables the advanced features option upon restart.)

3. Under Catalog > Quicksilver, check Proxy Objects.

Then this hint works beautifully! Great hint, by the way--much better than setting up an iCal alarm or some such nonesense for a quick reminder.

ok - so piecing-together helpful bits provided by others and expanding on them a bit for those less familiar with quicksilver, i will pass along my understanding of how this works. quicksilver gurus: if i get any of this wrong, please correct me.

(first, note that quicksilver behavior is dependent on what the way you have your preferences set, what plugins are loaded, etc.)

execute the basic display text message on your screen:

activate quicksilver (control-space by default)

hit "." (period key) to enter text mode.

type some text (any short string for this example).

hit tab to move out of the text window to the "verb" window or whatever its called.

type "large text". as you start to type the first few letters, quicksilver should search for matches. when it arrives at "large text", you can just hit return to select it and execute the command.

the text you typed should appear in large text on your screen.

ok, so now you have executed the basic (immediate) command. now to use the "run after..." feature, repeat the above procedure, but at the last step, instead of hitting return, hit control-return instead. this tells quicksilver that instead of actually executing the specified command, you want to treat the whole command (with arguments, etc.) as an object which can be acted on by other commands.

so after hitting control-return, you have the large type command and argument in the top window wrapped up as the "noun" and you are in the "verb" window, so you just type "run after" and quicksilver will complete your input. when you see "run after..." hit tab and then you'll be in another text input window where you can enter the time. i am not sure exactly what syntax is accepted here, but as a simple text, i typed "30 seconds" and it seemed to work.