SpaceX uses a different methodology for fueling, colloquially called "load and go". The idea is you load supercooled fuel (for maximum density) onto the rocket 35 minutes before launch. It's a methodology that has its risks
SpaceX uses load-and-go for its satellite and cargo Dragon missions currently, starting the fueling process just 35 minutes before liftoff. The company has adopted that approach because it uses "supercooled" propellants that are denser, improving the vehicle's performance.
That approach, though, attracted scrutiny after the September 2016 explosion of a Falcon 9 on the pad at Cape Canaveral during preparations for a static-fire test prior to the planned launch of the Amos-6 spacecraft. That accident, which destroyed the launch vehicle and satellite, was blamed on the failure of a composite overwrapped pressure vessel in an upper stage propellant tank.
So, why can't they wait? It's because the fuel gets too warm
That's because liquid oxygen is pumped into the Falcon 9 at a very low temperature: 340 degrees Fahrenheit below zero. That keeps it liquid and densifies the fuel, a type of kerosene called RP-1, which allows SpaceX to cram more of it into the rocket and squeeze more performance out if the machine.
Once inside the rocket, however, the fuel begins to warm up, expand, and boil off. That fuel loss starts the launch clock ticking.
"That changes how much performance you get carrying into orbit, and we don't want to cut into those margins," Insprucker said.
For a satellite, you can just pump the warm(er) fuel out and add new chilled fuel. But the ISS is a moving target
But [detanking fuel] is not an option for Demo-2, since the ISS flies over Earth's surface in a winding path, and at great speed.
"In the case of the International Space Station, an hour and a half from now, it's nowhere where we need to be to get to orbit," Insprucker said.