Try to get the biggest starting area and you will get as much time as you can.
Another cool variable is the pollution attack cost multiplier. I love to drop that to 0.3 or something along those lines. You will get a LOT more biters attacking you. Be careful about dropping it too low as it can cause the pollution cost of ammo get higher than the pollution cost of biters.
Theoretically you could mess with the pollution absorption, so the tiles/trees absorb it faster. Possibly (I didn't test this), if you increase the pollution absorption 5 times, maybe dropping the pollution attack cost multiplier 5 times could result in long-term comparable results, but with about 5 times more time to prepare? I'd guess there is some obvious caveat I'm forgetting, like the pollution costs for dying trees, the values when tree stages change not being affected, or something along those lines.
If you want biters to remain capable of causing damage even in late game, increasing maximum wave size helps a bit. In general, more smaller attacks cause less damage, while less bigger attacks cause more damage. Biters still won't utterly ruin proper defenses, but how would you defend from them if they did. :))