I don't think it will be possible to summon enough firepower to make it worthwhile except with maybe fallen spire. In the time it took to get 150 knowledge from the planet there were 1k zombies swarming.
Fallen spire may be possible for a short while, due to the current game layout. After 80 minutes I managed to knock out a mk IV planet 5 planets from my homeworld. I guesstamate at the 2 hour mark I'll have enough resources stockpiled to cloak in the engineers and colony ships to get there and quickly prop up defenses around the botnet there, before making it. With the botnet and ars and heavy defenses, one city may, may, be possible (doubtful, but even 4 frigates would help if I can't)