Put a marker where you want each bomb, and name the markers. In init.sqs put something like
pipebomb_1 = "pipebomb" camCreate getmarkerpos "marker1_0"
Create a trigger for each bomb: in the activation field put something like
pipebomb1 setdammage 1
and use the countdown fields as a timer so that it goes off at the right time. If you want the counter to start at the beginning of the mission put
true
in the activation field. I haven't tested this, so its not guaranteed. If it doesn't work the official and unofficial command guides should help.
As for deactivation, I don't know .... I know you can use actions to make a dude set them off, maybe there is a deactivation action ... though dunno whether that would override the setdammage command, I doubt it. What might work would be to have a little script that deletes the pipebomb and then replaces it with a new one. The new one would have different name so the trigger would not affect it.
Alternatively, use a variable in the activation field of the trigger: if explode=false (say) then the trigger won't fire and your bomb is "deactivated". You could make it so that if your guy gets within 1 metre then the bomb is deactivated. I think the command is "distance".
That's not very clear so I'll say it again. If the bomb is supposed to go off 5 minutes after the mission starts unless the guy gets to it then your triggers look like this
init.sqs
explode=true
trigger 1
condition: true
countdown: min=max=mid=300
activation: timer=true
trigger 2
condition: pipebomb1 distance player <=1 (check the syntax)
activation: explode=false
trigger 3
condition: timer and explode
activation: pipebomb_1 setdammage 1
Hope that helps.