After sitting overnight, car takes 30 seconds of cranking to start. After this, it starts right up unless it sits for 8 or more hours. Why?

When you put your key in, don't turn it all the way but to the point where everything powers up. You should hear a hum from the lower rear that lasts about 3 seconds. That's the fuel pump. If you don't hear that, it could be the fuel pump.

Sounds like the engine oil is quite thick when cold so you probably need to check the last time the oil was changed along with the filter.once it gets slightly warm the engine takes less cranking amps to turn over so it will start quicker.

Plugs, ignition wires, and all that stuff?

unhook the battery for 30 min

Batteries can slowly die , will start OK when hot , but when in cold weather , will give problems.

Could be crankshaft sensor.maybe needs tune up,fuel filter.

try fuel injecter cleaner

Low fuel pressure.
You need to check the fuel pressure on the first crank and watch it as it is running.
Requires a special gauge.
If it were just a starting problem I would say it could be a pump relay, but not if it runs rough for 5 min.
Might be a dirty filter or problem in the tank.

My 98 Jimmy runs on synthetic oil and starts well after sitting in cold weather. If the weather is the problem, try checking that. If it is warm... sorry no ideas.