I looked around if I could somehow achieve this with what's done.
Quicksilver User’s Guide, p 44
TODO: You can define combinations of triggers to do one operation on immediate press and a second on a press an hold. E.g., you can define ⌃⌘I to open your Inbox and a second ⌃⌘I trigger to Get New Mail if you hold it down for 2 seconds. (one key for mail, holding it checks for new mail and then opens it) You can also configure triggers that use two scripts, one on start, one on finish.
My activation hotkey is ⌘⎵ so if I set the same for a trigger with On Press selected and Hold for 1.0 s set I get mixed results.
After setting up the trigger each time I use this key combination it does something different
1. Launch Quicksilver service is started — although QS's already running
2. Run the trigger
3. Activation of QS's interface
n. It repeats 2. and 3 from there on
It gets even more quirky if I use On Release instead.