Android:Netrunner videos: http://www.peachhack.com
The Ambush Dashboard ability reads:
Once during the Overseer phase, open any door connecting a hidden room to the revealed portion of the map. Remove the door marker and resolve the room stack.
So the overseer can use it at any time during the overseer phase.
Does that mean the overseer can use it before spawning enemies? (Open a door, resolve room, then use dashboard abilities spawn enemies at new passages/vents)
Does that mean the overseer can use it before refreshing the dashboard? (Use the ability, then immediately refresh it before moving on to enemy spawning)
I believe that I can open a door before spawning enemies, but I don't believe I can open a door before refreshing the dashboard. However, according to a strict reading of the rules, I can't see a reason I can't use it before refreshing the dashboard.