What, you mean the entry delay?
If you simply want your wing to show up, oh, say 20 seconds into the mission, just leave the "Arrival Cues" field with "True" in there. This means simply that the wing will arrive; then set the delay to 20 seconds.
Now, if you want your wing to arrive, let's stick with 20 seconds, after the GTC Placeholder is destroyed, you will need to set the arrival cue to be the destruction of the GTC Placeholder. Alternatively, you could use a "Less Than" Logic SEXP for when the Placeholder's hull drops below zero (I would not recommend this method). Ok, once you've got your cue set up, there are 2 ways to set the delay. The first is to set the delay below the "entry method" field (the drop-down menu where you choose "Hyperspace" or "Near ship", etc). I'd advise setting the delay there. The other way to set the delay is to look at the "Is-Destroyed-Delay" SEXP; there will be a number zero above the ship triggering the SEXP- that number is the actual delay.
The timing is controlled from both locations. You can use whichever location you like better, but I'd stay away from using both together.
If that's not the problem, and your ships are trying to launch from another ship, I need to ask the obvious question- is the carrier ship actually present when the arrival cue occurs?
Perhaps you could clarify some more; there is considerable ambiguity in your question.
