30
You hit the last key on the control sequence and freeze, hands hovering over the keyboard. You can hear Natasha somewhere in the background of your head, urging you to run, Clint, run, but you know you can't yet - the sequence needs to be verified, Tony and Phil both said so. If you've punched it in wrong, the remote controls won't release and then the whole mission will be for nothing.
Natasha's still there behind you. "What are you doing?" you ask. "Run! I'll be right behind you!"
"No, you won't," she says. "I'll back you up." She isn't leaving until you are, and dammit, why isn't this sequence verifying?
There's a series of beeps. The sequence goes through, all-clear, green light, but as it does, the door bursts open and there's gunfire. You feel the first bullet, but after that you're numb.
The last thing you manage to say is, "Run, Tasha," because the mission is a success, even if you're not going to be around to get the praise. Natasha, you hope, still has a chance.