User blog comment:EliteMadness/Custom Champion - Vane/@comment-38393713-20190218075248/@comment-4091261-20190218135604

It depends on how long you are talking about. I believe the bomb could be active for a very long time, because it's actually kind of difficult to bait people into traps. Well, not difficult more than it just takes longer than you'd expect.

I think it would be pretty lame to have an ultimate just sitting somewhere and timing out without ever getting used. A couple examples of it being used in a reasonable way could end up like this: LOL
 * You throw the C4 somewhere in the backline so the enemy doesn't notice. However, your team just goes all-in and you advance forward instead of moving backward into the C4. The C4 blows up in the middle of nowhere.
 * You throw the C4 in a random bush in the jungle. Your team decides to just sit around sieging a turret while all the five enemies turtle as if it were ARAM. The C4 blows up in the middle of a jungle bush.
 * You throw the C4 in Baron pit. Your team starts doing baron, but is then interrupted by a fed . Everyone dies. Your C4 blows up Baron and nabs you a penta and that juicy bounty.

I feel like the times it could be useful would only be on the epic monster pits. Essentially, I believe that the moment everyone is in the blast zone, you as a player want to activate the C4 despite how long it has been. That's why I think full impact should be dealt when that time comes, just not as a clutch throw down your ult and instantly blow yourself up.
 * If you want clutch, instead of ramping up damage, the AOE could increase instead to max over maybe the first 10 seconds. Finally the trap would stay at max range until you manually detonate it. The damage would be the same the entire time.