Its not so much as rushing, I would say rushing is going full military and attacking without an established econ.  Anyone can get 15+ LRFs up (10 or so if Advent) and "rush" their opponent.  These sort of games usually depend on who can out produce the other, therefore if another has a slight advantage (3 mines on his 1st roid instead of his opponents 2 mines) then he would outproduce.  I understand your reluctance to this strategy becuase it relies alot on chance and map placement, race, in addition to actual skill.  "up-and-running" For me is usually within 15 - 25 minutes of "peace-time".  But I clarefy up and running a bit differently.  You will never have enough time to build your whole upgraded fleet supply in a multiplayer game unless the map is too big for the amount of people in it.  Instead, you should focus on the flexibility of your fleet, and scouting the enemy.  Here is an example of what I mean, most people build LRFs as the core offensive power to their fleet, your response to this would be toe to toe with your LRFs, which works... barely, or make the appropriate counters.  You dont want to blindly make a fleet without knowing what your enemy has becuase you could be happy sitting on a ton of LRFs and Carrier Support when your enemy rushed HCs.  But in any multiplayer game you should always just have the expectation of getting rushed.  And if you dont get rushed... great, now you have a bigger colonizing fleet and you can colonize faster then them... or attack.  Hope this helps!