[Screed's 'Once Per Activation' timing window.]

Assume I have Admiral Screed on a ship with Salvo and the ability to refresh it with Officer Reeva etc. and am being attacked by a ship and the two squadrons it activated. May I use screed on all three salvos? 

I'm looking for a bit of clarity on the timing window of "Once per activation..." text on screed. Since the squadrons are activated within the Ships activation, do I miss the timing window if I screed one of the squadron attacks before it is the ships turn to shoot me?  

Thanks!

[Obstacle movement and tokens/Mines.]

Can a token/proximity mine move from obstacle to obstacle through the use of effects like G8 experimental projectors or objectives that allow for obstacle movement?

For example, I have a token half overlapping an obstacle and open space, I then move the corresponding obstacle and token so the token is now overlapping 2 obstacles. May I then move the new obstacle and the same token?