About the countdown timer there can be lots of frames for each seconds----->each second = a frame. .for example 30 seconds has 31 frames from 30 to 0 and each frame shown for 1 sec.
For stopping it you can do something like this.
The object is "destroy the detonator".
The detonator is not spawn until you step in a trigger.
There are two other scripts set as main script for the detonator and other entity1(entity1 is outside the map and player can't see it).
The script of the detonator is :
If detonator spawn = 1 , entity1 spawn = 1
The scrip of the entity1 is the countdown script like this:
entity1 spawn = 1 , countdown start = 1
entity1 spawn = 0 , countdown stop = 1
countdown end = 1 , barrel1 addhealth = -20
.
(there should be a barrel to explode with the healths of 20)
After all when you destroy the detonator by shooting it's not spawn anymore and entity1 will spawn off and then because it's not spawn the timer will remove and the barrel wont say boooooooom.
I can't do all of these but I know how to do it.
(Sorry for bad English)
Have our guns was a mistake!!!
I am PaYaM