So I'm back to standard speed, playing like I'm at quick speeds. I'm usually good at doing 10 cities by turn 100, but I feel my campuses are too slow. Half the time they're in cities without woods or rainforests. The other time the campuses don't contribute much, like +1 adjacency bonus or something worse. I just feel like my science game comes on too late. When you plop down the science district in the capital and all the other cities, how long do you wait until you actually build it?
One of the secrets of the Science Victory is that unless you are playing one of the Civs with specific bonuses (Korea and Maya obviously, but also Australia, Inca, Brazil, Japan), it is a crapshoot whether you'll get a map that's suited to Campus adjacencies. Start bias is one of the most important aspects of the Civ you choose. That doesn't mean you can't win a Science Victory as say, Rome or Scythia, but you have to play the map. If you roll up as Mongolia and you get a bunch of mountain tiles, then yeah, a Science Victory could be a good alternative route. However, if you have a bunch of flat land, don't fight it. Use what the map gives you.
Remember that the Campus is probably the strongest District in the game, so you'll want a couple no matter what victory type you are going for. Keep an eye out for good Campus locations as you are expanding. 2-3 are plenty (for your average non-Science Victory type). The Government Plaza is also really useful for creating Campus adjacencies:
Government Plaza: +1 Science
Minor adjacency from City Center and Government Plaza: +1 Science
That means you can get at least 1, and probably 2 or even 3 +3 Campuses using the Government Plaza. All you need is a +1 adjacency from the terrain (so a mountain tile or 2 jungle tiles) which is pretty easy.
When do I build Campuses? That depends on the map and my surroundings. If I am going for a Science Victory, I'll build one early (around turn 20-30 or so) for the State Workforce bonus and to unlock research projects so I can rush Hypatia if I need to. The rest come in when it makes sense, which is usually right after I've built a Monument in the other cities (I'm focused on getting my tier 1 government ASAP more than getting Campuses out). I tend to build my army and my Settlers in the capital and my other cities focus on improving themselves. This can go out the window if I'm being crowded. So, maybe around turn 60-80 or so?