In the Star Trek: Voyager pilot, [The Caretaker](http://en.memory-alpha.org/wiki/Caretaker_%28episode%29), the *Voyager* gets stuck in the Delta Quadrant because they had to destroy the Caretaker's array, which was their only way back home. The explanation was that if they use it to go home, the Kazon would take it over in their absence and use its power to dominate the quadrant.

So why didn't Tuvok program the tri-cobalt device with a time delay circuit to blow the array after they go through? Federation warheads are [highly programmable](http://en.memory-alpha.org/wiki/Photon_torpedo#Other_uses).

P.S. Obviously, I'm expecting a possible in-universe answer, not "because that'll be the end of the series".