1) Invoke QS, hit period to enter text modes and type your reminder: e.g. "Check Oven," tab now to the second pane and select Large Type.
2) When you hit enter you'll get a large notification as follows (screen shot reduced):
3) Here's the cool bit: now invoke QS again, and in the first pane type "last," and select "Last Object," hit the right arrow and your last command "Check Oven" (Large Type) should appear.
4) Tab to the second pane and choose Run after Delay... or Run at Time... This will reveal the third pane, tab to it, and type in the delay (e.g. 45s or 30m or even 3m 30s) or the time (e.g. 7:15pm) as appropriate.
5) now at the time you specified (or after the delay you specified), the notification as in step two will pop up.
A few notes: For this to work you must have proxy objects in your catalog, which means you must "Enable Advanced Features" in the QS Preferences. In addition, you can interleave reminders if you choose one with remind at time, and the other with remind after delay (when I tried to interleave two reminders after Delay it didn't work for some reason). Finally, you can use the same trick to run any command, not just Text (Large Type).