Nah, after the fighter game is done, which lasts about as long as the initial scout/probe attacks for land, you go immediately to the bomber game (assuming the enemy does not, himself, have fighters). Bombers require a level of defense above what counters fighters: The defenders you made to beat fighters are totally useless, you need Hacksaws, Flak or Razors.
These more expensive defenses create a very small no-bomber zone, allowing you to operate outside of those regions fairly easily. If you've played well and saved your bombers, by the time you hit the mid game, for the enemy to field enough AA to shut you down from all vulnerable targets actually costs more than you're spending on bombers.
Though yeah, mid-to-late game, once the enemy has wasted all this money on AA, you should switch factories and kill him with land. You CAN always start using nuke bombers, which, again, take 2x as much AA to kill as precision bombers. As google says though, the main reason to go air is to make the enemy waste his metal on AA.
This is very different to going air as a second factory in the mid-game of course.
