There are of two minds in this, either a second cap very early.. (on your first fleet step up) or later. In my mind it serves are a good pushing tool and focal point for an enemy. If it can survive, you're going to be fine. If not then it's a waste of dps, fleet or money whatever you look at first.
I don't normally get a second cap ship, until 40-50mins past. Having said that it is map dependant and can be used to expand without having to babysit too much, For tec getting a marza and clearing planets is an excellent way to level it up, once they get to 6 they are beasts.
I wonder, the first 2 planets should be had within 1-2 minutes of the game, depending on your start, then you should be aiming for 4-5 and then a push or fight for a controlling/fleet planet (one to which you can use as a pushing base).
Ideally to answer your question, it's personal preference. I rarely get cap ships and prefer a more mobile and reactive fleet. Especially in 1v1s, When you consider how weak they can be early level, losing one is a serious hit to your economy.
